I often tend to extremes and have trouble with moderation. I like to do something all the way or not at all. I guess I have a bit of an obsessive streak to my personality. People often say that absolute adherence to a rule or view is extreme, but I think these absolutes are the best way to find moderation, or pickup a new habit.
What I've found that works best is to not give your self an out. For example, I'd often drink a bit too much, and wake up with a hangover, possibly regretting something I'd said the night before. Now, I have a 3 drink maximum, a rule I'm not allowed to break. It's just enough that I can still be social, but not enough to bring regret or lose my resolve and have to many.
I always said I wasn't a smoker, but I would on occasion, but only when I drank, or I had some left over from last night, or when I was hanging out with smokers. That's a lot of outs and it ended up being almost every weekend. That was my idea of moderation. Now, I have a simple rule.
I don't smoke.
There are no exceptions. Combine that with my 3 drink maximum and I don't drink enough to lose my resolve on smoking.
I never exercised enough, because getting started always seemed too daunting. I finally got my self to do it, off and on, a bit of running, or some pushups. But I'd always have some excuse and end up missing a day here, or a week there. Now I have a simple rule and a simple schedule. I do some kind of exercise 6 days a week. I run every Tuesday, Thursday and Saturday, and I do some other exercise, such as pushups every Monday, Wednesday and Friday. The results have been clear, and I'm sticking to it, because I can't break my rule.