There's not much to worry about. There are no trick questions or "hard" to answer questions that need to keep you up all night (although I was just from sheer excitement). Like the previous responders have said, be punctual and be truthful.
We were asked about 3 or 4 questions about when we intended to travel, where we intended to enter the country from, what sort of work we intended to find, and if my wife intended to give birth in the US (she was pregnant at the time). We were done in about 5-10 minutes.
All the best.