Okay, before I state the obvious -- that namlive has given really bad advice ( I guess I stated it anyway, huh?) -- let me remind everyone that you can't always tell whose tongue is in his cheek while he's posting here. Let's try to take things a little more seriously when the question is of a serious nature. Okay?
Here's what you do.
Be honest. Don't answer more than is asked. The tendency to expound at length when answering a simple question is a clear tip-off that you are feeling guilty. The first conclusion the shrink will draw is that the thing you feel guilty about is lying to him or her.
If you are going to be a nuke, you need to know this acronym anyway, so here it is: ATFQ! Answer The F***ing Question!
Answer each question. Then stop talking. A trained analyst will know exactly what questions to ask to get the information that he or she wants. Answer them simply, quickly and honestly. Don't explain - even though the shrink WILL PAUSE to see if you are going to explain. Don't take pauses as an invitation to talk. That would just be you digging yourself deeper. If they want explanations, they will ask for them, but they can get that information more efficiently by asking pointed questions. If he or she says, "go on," don't bite. That is another little trap that anyone can fall into.
Don't read into the questions. Nobody is accusing you or judging you, even though it will feel like they are. to a point, they are judging you. That is the reason for the whole exercise.
Accept the fact that they will find out all that they want to know about you, and that you are not perfect. No big deal. Nobody is perfect. In fact, trying to appear as perfect will be a sign of a deeper problem. Everybody makes mistakes, but the perrson who tries to rationalize them is a bigger danger than the one who knows they were wrong and admits it. The person who tries to justify and rationalize wrong acts is not trustworthy. Even the laying off of past misdeeds as youthful transgressions can be seen as rationalization.
Admit that you did wrong, admit that you regret doing those things. Be humble and contrite but genuine in your answers.
Good luck.