Two easy steps:
1. See what they do in the United States - particularly the more conservative states.
2. Do the opposite.
I was thinking about this tonight while watching TLC, which had a program comparing American abstinence-only education with the approach taking in the Netherlands.
This article also describes the divide within the U.S., and the way that abstinence -only education doesn't seem to make anything delay sex but does seem to make teens less likely to approach it with any sort of responsibility.
Now, I've argued that there are examples of effective abstinence-only education - but they don't come from American public schools. You will find the abstinence approach to be fairly successful in insular, conservative religious communities, because they don't just say "don't do it", but actually gear every aspect of a teens life toward making sure that it doesn't happen. There's no dating, no social contact with the opposite sex, no TV, no movies, no unmonitored internet access, no secular music, no books depicting boy-girl relationships, and no immodest clothes. As if that weren't enough, you also have kids attending private religious schools, so the home, the school and the religious leaders are all giving the same message. Early marriage (often arranged) is encouraged. It's a total lifestyle, and it's completely at odds with the way that most teens outside of these communities live. If there's any weak link in this system, it doesn't work and kids are vulnerable.
So, back to my approach.....
First, we challenge the dominant cultural messages about sex. The kids know that sex is fine for consenting adults - preferably married ones - but that it's not ok for until you are at least 18, it's not ok if anyone is being forced and relationships must be committed, non-violent and loving. I'm not remotely scary, but we do have rules and I'm not afraid to say "this is not appropriate". I don't care if the radio plays that S&M Rihanna song non-stop or if all the other kids get to wear mini-dresses.
Second, I don't think that teaching somewhat conservative values is any reason to avoid teaching essential information. In fact, I don't shut up about it. I want my kids to have information way before they need it, to have all of the accurate information, and to know that mom and dad are more than willing to talk and answer any questions. Of course, I also know that the idea of talking to my parents would have horrified me, so they will also have the number of their family doctor and local clinics as well.