I've recently been trying to change my habits.
"Doing the same thing over and over again and expecting different results is the definition of insanity." - Einstein. Maybe. No one ever seems to know where quotes come from these days.
Anyway.
I'm finding the tool that is most helpful in keeping my self accountable to the changes I want to make in my life is keeping a journal. I journal about how I feel everyday so if a activity is good for me then I'll have reinforcements by looking at my journal and seeing whatever positive effects it's creating in my life. If you are trying to lose weight you can track calories and weight and see a correlation, but the same can be said of emotional states. Some days I'm more productive than others, some days I am happier. I'd like to have more of those days, so trying new things, or stopping old habbits, you can reviews your mood day to day and determine if the things in life you are doing are actually good for you.
If I feel like giving up on it quitting a bad habbit, I know I will have to write down that I gave up on it in the journal the next morning. It is a way of keeping myself accountable to myself. It also creates a similar affect as the Seinfeld Calender, so if you are writing about your experience in changing a habit, you know you've already put a bunch of effort into writing about your experience. It becomes a project you're in and not just a whim where you say to yourself "I'm going to do (insert thing here) everyday". When you're writing about the experience every day, you add weight and momentum to it which makes you less likely to just give up on it.
It can also give you a reason to stop doing it. I stopped taking sugar in my coffee years ago and I found it life much better, I didn't have that huge 3 o clock crash everyday. I haven't used sugar since. Then I decided to see what going without coffee completely was like, and after reviewing the time I spent without coffee, how I felt during the day, I realized I didn't feel removing coffee from my life was of any benefit.
One of the best things though is writing all the thoughts I have every morning, not just about habits, or things like that, but any thing kind of empties my head of all those random thoughts floating around. For some reaosn when you write it down it's like you're really acknowledging the thought and you no longer have it as background noise in your brain.