This a situation of struggle myself, even though we have all the steps to follow, it will be hard to steak them in a long term. I think, at first, we need to be very conscious about what we want to change and why we need to change. After it, we should break down the steps to baby steps.
The first change could be the one that affect that individual person the most. Going to bed everyday at the same time, for example. Our body likes routine, so giving it bedtime routine is a good start. After mastering it out, we should go the next critical part.
A good control of improvement is good you feel the nest day.