I’ve struggled with this for my whole life (which has been a while now) and haven’t succeeded in developing my willpower much at all. I think it’s just part of your ‘personality’. In quotes because you can change your personality somewhat with therapy or other growth techniques, but still, it takes a lot of work and there is no guarantee it will happen.

That said, I do use commitment devices to substitute for willpower sometimes. One that works for me is to join a class or group for exercise or other things. In my case it has worked for meditation, exercise, martial arts, and others. I find that when I wake up and feel like ‘I just want to lie around and play video games all day’ I then remind myself ‘the folks at the group will notice I’m gone, I’ll have to explain it, and It would feel better to just attend’. And so I get my exercise. Usually. If my brain can convince me I’m not feeling well I still skip out sometimes.