Best way to quit smoking is to have never started in the first place.
My older brother is still trying to quit though.
As for coke, I've tried it before at a friend's party, and to say the least it wasn't my thing, not to mention that it's very addictive. However, some of my friends do it every other night, and shrooms and acid just make me shake and go ape**** so I stay away from that ****, I'd much rather roll than trip.