What magnifies the problem is if a single mom or dad does not have the time to be involved with his or her child or to notice what's happening. Mainly, a very solid concept of what is right and what is wrong. Set some parameters, not when they are teenagers, but when they are as young as a year old. Also, set up good communication between you and your children. As they grow get your children involved in a lot of activities with other kids who are on the right track.
Church is a good place to look.
You can also try school band, athletics and a number of other groups. But don't be deceived drinking and drugs can be a part of any of these. Just because they go to church each Sunday doesn't mean your youth group kids are clean. Get your kids busy, but be involved, too. Kids want acceptance from their parents, but there comes a time when they need it from peers, too.