{random internet advice}
Our main strategy has been the same as for non-internet safety, talking about sexuality, drugs, and crime since the boy was young and normalizing those discussions to create a context of trust. Our theory is more less that the only proven method for creating desirable behavior is to help a our child learn to make good decisions.
So far, it seems to be working reasonably well. It's not that he doesn't form typical teenage judgments from time to time, but there's a foundation for conversation and a history wherein listening to our experience has proven to him to be worth doing via independent verification.
tl;dr Talk with your kids now and it will be easier to talk with them later and more likely that you will be able to discuss potential issues when they first arise rather than when they become habits.
Good luck.
