Atomic habits is a good book about this. Tldr: small successes. Discipline comes form making the bad habits hard and good decisions easy. Example: delete distracting apps, put fruits on the table, hide the snacks, put the todo list on the door on your way out, practice going to the gym by just putting on your shoes, going to the gym, spend there 5 mins and go back, then slowly increase, reward yourself for small progress.