If you want to create change in your life, you'll have to get good at identifying and removing your own stumbling blocks. In essence, you want to make it hard to do what you wish to avoid and easy to do what you want. Being carfree provides me with tons of examples of this in my own life. If exercise required me to go to the gym, it would never happen. Never. But lucky for me, it is hard for me to get through the day without at least a little exercise -- after all, I have to walk or bike anywhere I want to go.
Anything that you want more of in your life should be almost impossible to avoid. Anything you don't want in your life should be easy to avoid so that you are not tempted. Want to use your car less often? You could try parking it far away, loaning it to friends regularly, or keeping the tank at a quarter full (making your car easy to avoid). At the same time you can get your bike tuned (and keep oil on hand), research all the spots within easy walking distance where you can run your errands, and get a bus and/or subway pass (making walking and biking easy to do).
Want to spend less money? Don't go in stores except when absolutely necessary. They only want to sell you crap that you don't need. Consider carrying and spending only cash (which seems a lot less like "play money" than a credit or debit card). Discover your gazingus pins and then avoid gazingus pin stores like the plague. Don't watch TV or read mainstream advertising-driven magazines. Find a carfree route to work, practice it for a little while, and then sell your car. Trade in your cellphone for a prepaid (or get rid of it entirely). Cancel your broadband since the internet is both wasting your time and selling you things (hypocrisy alert: we are on the verge of getting non-dialup internet at home for the first time).
What do you want to change in the year to come? Once you know what you want, make a list of ways you can remove your stumbling blocks, making it easy to take positive steps and hard to backslide. Whatever you do, don't rely on willpower, which I'm pretty sure is just a myth.