Old habits

Ever try to break your self of an old habit? Something that you have been doing as long as you can remember, which is saying a lot considering I can remember being five years old. It's not an easy thing to do. How do you stop your self from doing something that you don't know your doing until it's to late? I'd really like to know, any advice would be welcome. I've been trying to break my self of a habit my wife can't stand for, well longer then we've been married, and I haven't managed it yet. So, anybody that can lend me a hand, it would be helpful.

I would really like to be able to stop, or even recognize the fact that I'm doing it.