How Exciting!
I went to the temple for the first time 2 years ago for Janmastami, and have been back every week since! I would just advise the same as everyone else, don't wear anything revealing, no tank tops or anything. Like the others said, it is our biggest celebration, so be ready to have a good time, dance, and feast for Krishna's appearance day!
Find someone friendly and maybe you can ask them any questions yo have about the temple, or if you are going with someone who goes, ask them.
Have a great time and please come back and tell us how it was!
Hare Krishna