I smoked for 2 years, then I just quit cold turkey. Didn't smoke for 2 years after that. Then, I kept partying and getting all messed up all the time so I started again - kinda. I have about a smoke a day unless I'm partying now(in which case it could be 1-2 packs..). It wasn't tough for me to quit for the 2 years though - I just said no any time anyone offered it to me, and I never bought any of my own. I concentrated on other things and always said no even when I wanted to say yes. Just don't give in.
Its not all that complicated. -> if you REALLY want to quit, you can easily do it by saying no. I don't really worry about quitting anymore, because I'm young, I drink and do other bad things that I shouldn't do but I will definitely quit before i'm 30 or married, or whenever I don't feel like doing it anymore(or when it just feels weird for me to do it cuz I want to quit so bad..). I know it won't be hard for me, because I've done it before. I'll just do the same as I did before when I went w/o a smoke for 2 years...
Tell yourself that you are a NONSMOKER and it would inflict on your values if you put a cigarette in your mouth. As soon as you don't think in this mindset anymore, you will find yourself giving in, so just consider yourself a nonsmoker, and stick with the mindset of a nonsmoker. Would a nonsmoker put a smoke in their mouth? No, so from now on you are a nonsmoker -> ACT LIKE ONE!