Easier said than done, I know. I use an example from my own area of weakness. When I go to Weight Watchers, I find it easier to avoid the temptation of indulging in my favorite food if I don't go the the ice cream parlor. The same is true for sex. Steer clear of parties or situations where making out for hours is the only entertainment.
Nobody is made of stone.
Setting limits is easier if you're not face to face with temptation. A year ago our local newspaper ran a series entitled Teen Sex. I was fortunate enough to be able to pull together several different panels of young people for discussions that were quoted in the series. One set of students was made up of seniors who were abstinent. Pictures and quotes from these young adults were featured in the article.