Main tip is enjoy it man
It's all about having some fun so don't stress about stuff.
If its scenario, try and latch onto a group of people who have done it before. They will know where to go, and what the general plan is. Nothing worse than just running around like headless chickens with no idea what is going on!
Don't panic about gear. Things tend to go wrong when its your first time, but there will be loads of people willing to help. In fact that's what some people love doing! So if your stuck for something or aren't sure about something just ask. Even if the first person you ask isn't helpfull or is a bit of an arse, there tend to be more helpfull people about than idiots. They where all new to this game once so most people are happy that the sport is growing and will help sort whatever it is that's wrong.
Don't forget rule number 1......... Enjoy it
Oh and if you enjoy a few scenario days, why not at some point try a tournament! You never know, you might just love it