If you have space outside, plant native trees/vines/bushes that will help shade the building from the sun if you're getting direct sunlight. You can just do clippings from wild growing plants for free.

timing of the windows opening and closing is key. Also tracking temperature helps, just a crappy thermometer (one indoors and one outside not in sunlight) will let you know when it's time to open or close up.

Concrete/bricks work both ways as a thermal mass, if you can get them cool and covered from the sun it will help cool your area (think of cold concrete floors, I have an inner brick wall that an extension was built out on and it stays coolish). Same with water, most have experienced a cold water pool/pond on a hot day, big blocks of frozen ice can do the trick if you stick to freezing at night.

Free stuff:

• No/less electronics during the day (tvs/chargers/computer), it all adds to the heat
• no cooking during day, cold cuts/food only till night
• Take a nap during the hottest part if possible, or just sleep in daytime and move about at night on off days (something about waking up after a nap makes it seem less overbearing)
• do maintenance on your fans, take them apart and clean/grease anything that needs it (will need to clean more often if you lubricate due to dust build up causing gunk)

Black-out curtains are great to stop light, but if it's entering the window already it's just heating up that one spot so you're still technically getting the thermal radiation. For that fix you would want reflective window covers, even foil would technically help slapped to the window (it's the only time those reflective insulation boards actually do anything with infrared). Foil with something behind it to insulate, like literally anything (cardboard wrapped in plastic to air seal can even do it), then you can take down your contraption at night to let air through to cool.

Insulating and air sealing. Alternatively, air flow in any spots building more heat than the outside temp (like an attic or upstairs area). If it's a family owned place it's easier, renting you might have to address concerns with landlord.

Currently temps in my area are getting about 95f(35c) daytime and 65f(18c) to 60f(15c) at night. I can usually get my house down to 68ish(20c) before the sun comes up. Windows in a bottom floor with fans pointing in, any windows upstairs with fans blowing out (hot air rises, it's the same technique for american colonial/victorian houses with dormers emulating ancient style architecture for passive cooling). If it's single story just be aware of wind direction if you're using the fan method and point some in where the wind is blowing and pointing out at the opposite side. My house will at max hit about 80f(26c) but by then it's time to open the windows because the sun has set.

At some point, once true-true summer hits, the nights will be about 80f(26c) and over 100f(38cish) during the day. At that point regulating your body and getting used to the temps is key and an A/C or sometype of ground thermal air flow is the only way you're going to make anything cool. If you're using A/C just seal the crap out of your windows with plastic and/or insulation (remember condensation like an ice cup though will cause moisture and mold/mildew growth on the exterior if not done properly). Pick a room that keeps the coldest and put whatever you can on the walls and windows (even a quilt on the walls will help insulate some). Seal up as much as possible and hide from the heat.

I grew up here in Florida without air conditioning until I was about 25.

Really just learned to be still, that helps. Keep the windows open at night if it cools off at night.

Stay in the shade, if there is a breeze it is not bad. Fans, fans, fans. Carry a parasol if possible . Shade helps so much.

And I wait for the rainy season, ours is at the same time of year yours is. Love that time, every day it gets hot but then in the afternoon the rain comes.

ETA I think India has this covered already but stay away from synthetic fabric and cotton. Linen or silk are best, and oddly, light merino wool in a loose fit is also so good in the hot weather.

So, a lot of this is duplicated, but it's a list of what I do against the heat ...

External shutters outside of the windows, both are closed the moment the sun hits to shut in the cold(er) air, and open over night. We also have tiled shades over all the windows so there's no direct sunlight into the house during most of the day.

Ceiling fans running at low speed

Cold 2 minute showers in the middle of the day

Put on a cold wet t-shirt

Wear as little clothing as possible while out of the sun. In the sun, light coloured breathable loose material (linen trousers are a godsend against mosquitoes)

Don't go outside or be active in the hottest part of the day

Don't eat much, if at all, during the day

And my wife's favourite - getting in a kid's paddling pool (I don't like it, but she does)

Using IR blocking films (like the ones that they use to tint car windows, preferably the type that use static cling instead of adhesive because they're far easier to apply) on any windows helps to keep the incoming heat down during the day,

Having airflow through the house at night with open windows or some form of vent, just make sure to add in bug nets to block any intrusive animals.

The addition of louvres (solid panels that have angled plates in them to block sunlightbut allow airflow) to the outside of windows can help keep temperatures down as well.

Whrere I live, temps go in the 40-50°C range in the summer (and 60+ in some inland areas). Here is what we do to stay cool.

1. Cool(er) air ventilation Windows open at night, closed past morning, with blinds down when sunlight starts hitting the windows. Ensure that air can circulate through (otherwise, you might actually get heatstroke from how hot the house gets). In cass the heat makes you feel like you cannot breathe, blinds down and windows open (better than suffocating) Also, no joke, get greenhouse green screens, and set them up inverse outside your windows. Instead of trapping heat in, they throw heat out instead. Surprisingly cooling.

2. WATER AND COOLING FOOD! Water is a must, and there are foods that cool you down instead of warming you up. (avoid the later wherever possible!) Examples of cool foods: frozen desserts, lassi (yoghurt water drink, makes you sleepy) etc

3. Fans. Fans everywhere. Doesn't matter if hot enough that it feels like a hair dryer instead. Evaporation + air is your friend (bonus tip: if you live in a dry zone, get an air cooler. It's an enclosed fan behind a self contained waterfall. Humid air is particularly cooling. Beware metal cabinets in the same room though. They rust, bad).

4. Baths. Baths are especially cooling. Take at least 2 a day. My cousins, who live inland at 60+ temps, bathes at least 4-5 times a day. Also, their bathrooms all have massive fans :)

5. Clothes. In summer, we wear our thinnest, oldest cotton clothes possible (aka, almost seethrough). We never go out in them, but they sure make the house bearable.

6. Naps and talcum powder. Human body temps naturally decrease when napping. Talcum powder, spread on the hottest parts of the body, absorbs heat and cools you too. The powder gets soaked in sweat and is useless pretty quickly, but combine bath + fan + powder + nap (and probably no undergarments/naked) makes noon bearable to go through. Talcum powder in particular stops rashes from too much sweating, if you have trouble bathing more than twice a day like I do.

Thats about it from me. Hope it helps!

Things me or my parents would do those 40⁰C+ days:

Pull down the blinds to block the sun during the day. If the air is considerably hotter outside, don't open the windows/doors. Wait until there is no difference in temp to do so.

If access to water isn't an issue, once the sun goes down you can hose the exterior of the house, walls and any surrounding concrete/stone surfaces. It will cool it down considerably.

If it is really hot I would sometimes put a wet towel on wherever I was feeling the heat the most (usually heads and shoulders/arms). You will need to soak it every hour or so, because it will start to dry and warm up as you wear it. You can sleep like this, too, but you may wake up from the heat under a hot towel that's nearly dry.

Lie under a damp towel with a fan on the towel for evaporative cooling.

A/C is great if you can get it.

This isn't going to be an option very often, but when the conditions are just right I like to leave windows open overnight to cool down the house. If it's going to be below 60°F and above 80°F the next day, it works best for me. Keep an eye on the dew point though because too much humidity isn't great. I like to open windows on one side of the house then open another in the other side with a powerful pedestal fan sitting about 4 feet away. That seems to work best for moving air through the house and usually lets me get away without running the AC the next day. Also, Vornado makes a transom window fan that fits snuggly in the window case, that's a great balance between blocking out a bit more noise because the window isn't wide open, it's a noise machine, and a huge benefit is it's reversible.

Good luck!

stay inside naked

Try bamboo sheets. They are a bit expensive but they feel cooling in the summer, they are very breathable but are also have a weight to them to help you sleep.

In tropical countries I carry an umbrella everywhere. It's much better than a hat because it has more airflow and provides more shade.

My area isn't the hottest, but it does usually get up to about 100F for a day or two most years, and in the summer temps are in the 80s or 90s during the day pretty consistently, and it can be humid.

I have a mostly finished basement, I'll spend a lot of time down there over the summer, it stays pretty consistently cool.

I'm lucky that I work night shift, so it's easier for me to do stuff in the evenings or early morning before it gets too hot.

There's a saying that there's no such thing as bad weather, only inappropriate gear. I usually joke that in the summer that means air conditioning.

But if you don't have a/c, opening your windows and getting some fans going can really go a long way to keeping your house cool.

Limit your time outside, find somewhere to sit down in the shade and take a break if you need to.

Dress appropriately for the weather, lightweight, light colored, breathable clothing, linen is great if you can find it. Maybe consider wearing a wide-brimmed hat to keep the sun off your face and neck when you go outside.

Drink lots of water, find some cool foods to eat, watermelon, cold soba, ice cream etc.

You can dig a tunnel that is at least 6ft down and 100ft long that leads into your home at one end and up to a narrow opening on the surface on the otherside. Then add a fan that blows air from the tunnel into the home. This will function as a natural AC unit. It is a lot of work to accomplish but can cheaply cool a home as long as its maintained.

The science behind it is that the temperature under the earth past 6ft is around 55 - 65 degrees Fahrenheit depending on your region of the world. The fan will then draw the air through the tunnel where its cooled and pushed into the home. The tunnel doesn't have to be that big just like 2ft in diameter. Though mold can grow here so you would want to use a material that is resistant like a smooth walled plastic pipe for your tunnel.

The temps in Houston are now firmly in the dangerous range during peak summer. When you reach a certain humidity and temperature, your body can't regulate its internal temperature by sweating anymore, you essentially have to have some kind of external input to cool off, that can be cold(er) water, air conditioning, fans (where you can have lower humidity or temperature air blowing over you, or something similar.

If you can make changes to your structure, doing a radiant barrier or some kind of false roof (even a solar shade or something that doesn't block all the sun) over your existing roof to limit the solar heat transfer to your structure can help.

If you can get some insulation for the windows, especially if you can get the foil lined version and direct the foil outside, that will also help.

Local air conditioning (mini splits or single room units) are often less efficient but if you are just focused on making it tolerable, you can do a single room as a cool down room for less money (upfront and in energy cost) vs a whole house or multi room unit. There are 12v units that can be run on a decent size solar setup like used in RV's or campers.

Look into green roofs.

Might be a larger project to get started, than simply buying a fan, but will probably last longer and improve air quality as well as reduce heat. Even better if you can get your neighbours involved and give multiple homes green roofs together, to improve outdoors heat and air for the whole neighbourhood as well as for you individual home.

If you have access to a freezer.

Freeze icepacks and rotate them to your pockets, or sit them on your main leg artery.

Freeze a flat amount of ice and then place your feet on it to cool down.

--//--

Also the cooling neck-wraps with gel-beads, actually work to cool you down. Goes well with a fan blowing on you too.

If your home isn't well adapted to reject heat, you can use tinfoil to reflect the sun. It's cheap and incredibly efficient at keeping heat out. It doesn't look very nice but it works a treat. Just remember if you are covering windows (with anything) that the cover has to be on the outside otherwise some heat will still make it in.

Fans. Keep a paper/manual one on you are all times, as backup if you have a battery powered one. On those do your research to find one with a good battery.

If you're running your A/C you can set it at a higher temperature if you run a ceiling fan or upright fan at the same time.

Don't wear black or dark colors.

Cooling packs in the freezer, wrap a towel around it, put it on your head, hold it on your hands.

Just a wet cloth around your neck is great when you're out and about.

I grew up somewhere where it didn’t cool down a lot at night and the only solution was to sleep in front of a fan. Sometimes I could get the fan to blow directly into the sheets and sort of balloon them out which was pleasant.

Where I live now it cools at night so I can open the windows at night and close them up during the day. Sometimes I close the curtains too if it will be extreme. I open the windows and create a cross draft when it cools down.

Those ice/fan pseudo a/c setups don’t work well.

Spray your back and socks with water occasionally. Not the shoulders, that gives you rheumatism. Only works under max humidity of course.

In 105+ summers in texas we just crank the AC

The Hongkongers answer, "Air con."

I swear we abuse ACs way too much. Nobody cares enough about the energy consumption except Lam Chiu-Ying.

Obligatory not a fix for everyone but:

I've read that drinking cold milk helps keep you cooler than drinking cold water. Something about the electrolytes in the milk making it digest more slowly?

This is only a short-term fix obviously, and only if you enjoy drinking milk, but it's an option.