I smoked from about 16 to 22, as well. I started again a while back for about 2 months but stopped again cold turkey. What I've found works the best for me is, to replace the cigarette with something else. You've gotta still give yourself a reward, since that's the mental connection with the cigarette which will cause your mood drops.
Some people use altoids, gum, or candy also since those can be substitute as an oral fixation. I just substituted my cigarettes for hot chocolate, mints, candy or gum for a few weeks and I eventually stopped even thinking about smoking. Once you get to those 3 weeks or so, you'll start feeling much better and you'll start noticing the smell on your clothes which will help deter you from picking it back up in the future.
When I started again, for a few months, I was working in a restaurant; so I used the smoke break as essentially a way to go outside and get away from the drama/stress temporarily without being bothered. So, just make attempts to avoid said situations, if at all possible, or bring along something to use as a stress reliever.
The hot chocolate worked best when I was stressed and wanted to go outside on my porch, the mints worked best when I wanted to emulate smoking by breathing in the mints through my mouth, the gum worked when I just needed a quick fix oral fixation substitute. You can also substitute popsicles and so forth since the summer's coming up. Toothpicks also work for some people, as well.
My vice however, is if I'm drinking, it's hard to deny a cigarette. It just goes together so well. I have had one here and there when drinking but didn't crave one the day after. I also don't drink often, generally only socially. Ideally, you should just stop completely but I don't think it's the end of the world if you have a few on occasion like that, just avoid buying your own packs. If you have roommates/friends who actively smoke, try to avoid hanging out with them until you've hit that point where the smell bothers you, otherwise it'll make it increasingly difficult to quit.
If you want to quit, you'll quit. Get some gum/mints and hit the lab or stick to other activities which involve BOTH hands; I smoked like a damn chimney when I played WoW because hey...90% of the time I was idle doing nothing and I'd get bored.
