Turn whatever you’re trying not to do around and do the reverse…
Eating like crap? Focus all your energy into eating well.
Not exercising? Focus all that energy you use stressing over it into walking, running, lifting, swimming. Anything that gets you moving.
Trying to stop biting your nails? Focus everything you’ve got on manicuring the hell out of them.
See where I’m going here? It’s not rocket science. It’s Just Do It science.