Those of us raising kids are attempting this task in a much different environment than we were raised. The technology age has its upsides and....major downsides. Inspired by the book "Strong Fathers, Strong Daughters," my wife and I have organized and articulated our approach. I realize these rules might not jive with everyone's convictions, but they're a good starting point for us. If anyone has more wisdom/experience/feedback, we're open ears.
The primary principle I learned from that book is that our protective instincts are there for a reason. Our children might not appreciate the guidelines right now, but eventually they will find comfort in the fact that we are protecting them in love. It's a profound and noble responsibility.