Ah, it is A LOT easier said than done.
I'm now 16 and I still smoke, I started when I was 13 unfortunately. I tried my first cig when I was infront of a load of friends, to look 'hard', and didn't like it, but still I continued to smoke it as I didn't want to feel left out.
Now 3 years down the line I feel like a twat, and wish I never smoked my first one.
I always say to myself 'ahh, this will be my last pouch of tobacco I'm buying EVER', then a few hours later I go out and buy another packet..
One day I hope to succeed. It's the same with cannabis unfortunately.