Lying is the ultimate offense

When my kids grow up, I hope they will trust me with their inner thoughts and secrets.  I'd rather hear from them that they are struggling with an issue at school or that they have experimented with something they shouldn't have. 

So if that's what I want say 5, 10 years from now, how can I foster that now? 

Praise telling the truth more than the punishment for the misbehavior itself. Encourage your children to tell you the truth about something they did and when they give you the honest answer, hug them and tell them how proud you are that they told the truth.  Tell them how important it is to tell the truth.  Explain that they are still in trouble and must go to their room (or whatever the punishment is) but that when they are done, you want to give a jellybean (or some other reward) for telling the truth.  Eventually, telling the truth is easy for them because it's better than not telling the truth.

Conversely, if you think they should know better, punish them for telling a lie more than you would have punished them for the misbehavior itself.  Lying is the ultimate offense.

Some kids will take to it easier than others.  But by the time they are able to keep big secrets from you, hopefully they will have learned that they can trust you to be fair.

By the way, I have no idea what I'm going to DO with the information that my teenager spent the night drinking and partying.  But I figure I've got some time to figure that one out.  For now, I'm just focusing on getting them to tell me that when the time comes.