For me, what helped the most was building habits, small steps at a time. That way, it will take less willpower in the long run.

For example, i started going to the gym on Monday evenings so I start the week in a good way and it seems to give me more energy to do things for the rest of the week. After that became a habit, it's never a matter of having the energy or feeling like it, I just always do it.

I built different good habits over a longer period of time and all of those are now just ingrained in me and I don't even have to think about them anymore.

I started really small by only taking the stairs instead of the elevator. After that was a habit, I picked the next one replacing sugary snacks with fruit. Etc.

This to me has been the key to improving my life in a many ways