Played high end competitive paintball for the last 10 years up till season before last.
Firstly remember it ain't serious you're there to have fun, laugh at anyone taking it to seriously.
Never under any circumstances remove your goggles whilst out in the playing area, you might not see very well for that game but it's better than never seeing well again!
Don't pick up paint even if it looks ok, the moisture will instantly get to any paint on the ground, causing it to swell and at best jam in the hopper feed neck (no paint feeding) or at worst jam the marker or explode in hopper (goo in hopper can't be fired, will cock up your accuracy and ruin your game)
If you have some low profile soft knee pads you will do well wearing them, an adrenaline induced dive onto roots/flint will smart some.
Thin full finger gloves are a damn good idea
very baggy jersey (doesn't have to be thick so a dh longsleeve shirt would be good) you'll probably be given some form of coverall or old army kit so this may not be that usefull.
I hope you have a blast, i played my first game at a site and it led to some amazing times over the last 10 years.
Al