You are your habits. If you succeed in temporarily changing these you will eventually be a new set of habits.
Here are some tips I know work very well for myself to succeed in this:

1. Decide what you want to change in you life (ie become more fit / quit smoking)

2. Decide how you want to do it, make a plan (ie starting tomorrow I will work out minimum 1 or 2 times a week / reduce one cigarette pr day starting from tomorrow and full stop on date dd.mm.)

3. Introduce a whip (ie every week I fail to deliver the goal pr week I will have to pay a given sum to a person, pay into a pot or similar). It's good if it will hurt a bit to don't deliver.

4.Introduce a carrot. (Ie If I'm able to do this in at least 25 og the next 30 weeks.... / when I've been clean for 10 weeks...
...I will buy myself a X, travel to X etc.

5.Communicate what you are now going to do to all significant persons in your life. Your goals, what will happen if you fail, how you will reward yourself if you succeed etc. This I the most important one. If you tell your network it will become a lot more real and harder to first regret and after fail.

1. As your network are getting informed, see if you can get others to join your new regime. You may know others in the same situation that also could need this. If you succeed in getting one or more companions all involved will benefit from it. You can support each other on the way and ie agree to pay into a pot if you fail, a pot that will eventually end up sponsoring a big reward

Good luck!