I think the best bit of advice my instructor gave me before mine was 'enjoy it', and after the initial moment of disbelief as I left the ground (for some reason I seemed to think the aircraft would refuse to take off without the instructor sitting next to me!), that's exactly what I did!
The only other thing to say as others have is don't be afraid to go around if you're not entirely happy - I did as I had a bit of a bounce on my first attempt...