The biggest key to preventing teenage pregnancy is education. The more your child knows about sex and the realistic effects it has, the more likely they are to make good decisions. Assuming that if sex is not discussed in your home your child will abstain is dangerously false.
Be open about sexuality. After all, it is a natural part of being human. Be approachable! Let your children know that they can ask you any questions they have about sex, including intimacy in their relationships. Regular conversations that are in good humor for both parties will keep the lines of communication open.
While you work to educate your children about sex, it is also a good idea to establish rules as far as curfews and behavior go. The two work hand in hand.
Most importantly, work with your children to find activities and goals that will keep them busy! Teenagers who become pregnant often lack activity that leaves them feeling gratified - and they turn to sex. Discuss their goals and dreams. Encourage them to have activities outside the house in positive environments. Maintain the idea that education is the most important part of being a teenager!