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.