Gradually cut down by avoiding locations/situations you associate with smoking (if you don't smoke in your home or car, that's a huge head start - if you do, start there). You'll have to exercise some willpower to NOT give in to temptation, but you've already demonstrated you've got that. You'll slowly disassociate smoking from being part of your regular life.
I used to be a pack-a-day, in-all-situations smoker. Today, I smoke only once a year, when on vacation. I will smoke 2 or 3 packs during a 1 to 2 week vacation. In other words, I am NOT a non-smoker, but have cut my smoking down from 365 packs/year to 3 packs/year.