Firstly, you've taken the first step by asking for advice! If it's in your head that you know what it is doing to your health then now is the time to really give it a go!
I smoked for years and one day decided that I should no longer do it as I felt constantly unwell.
My advice would be dont just give up, plan to give up.
I planned to give up one year before I actually kicked the habit. Every time I lit a cigarette for that whole year I would tell myself that they were disgusting, and actually making me ill.
I continued this for the whole year, and two weeks before the day finally came I went to my doctor told him that I was going to give up on the date I had decided (happens to be 23/3 last year) and would need whatever he could give me to help.
Firstly he put my on Champix, I had take tablets, something I dont do very well, though I did take them for one week which helped immensely, secondly, he put me on the nicorette patches, highest level and then gradually took me down to the lowest level, I am glad to say that I still do not smoke.
The best other advice other than using your GP is phone a friend whenever you get desperate, walk your socks off when you get desperate, try not to eat more, this is my biggest challenge now, losing the weight that I have gained.
Whatever you do make sure that you really are ready to give up, I tried twice before and didnt plan just stopped smoking and lasted 6 to 8 weeks on both occasions, but this time I have succeeded and I know that I wont smoke again.
Take a look at my other hubs regarding quitting smoking they may help and please let me know if I can help further.
Good luck and set your date sooner rather than later if your serious about giving up.