Some simple but strict rules that help me are

- No food before noon

- No alcohol on my own

- No coffee before spending at least 5 minutes outside in daylight

- No driving to work (cycling or walking only)

- Cold showers only

Some more I've tried and would like to stick to more, but they seem too difficult and I keep lapsing after a few weeks:

- TV/Netflix only while stretching

- Work only after a gym workout

- Drink a pint of water before each cup of coffee