I tried to do a bunch of small things. No single thing was the key.
- started drinking my coffee black
- drink more water, and drink water instead of other things
- I take the stairs instead of elevator/escalator whenever possible
- I try not to eat seconds at dinner
- "Real" exercise (like running, rowing, etc.) every other day, but if I can squeeze in extra ones, (e.g., 2 days in a row), I go for it
- If I'm not up for real exercise, I'll go for a walk
- intermittent fasting in the mornings, so often no breakfast, but not necessarily every day
- No snacking after 19:00
- At restaurants, if 2 options look good, go for the one with fewer calories
There are probably more, but those are the kinds of habits we're talking about.
Also important: if you don't stick to all habits, don't beat yourself up about it.
With the above, I was able to get from a high of 235 lbs down to around 180. I'm a bit more than that right now, but pretty close still.
I had to look up:
HHGTTG = The Hitchhiker's Guide to the Galaxy.