As a paintball site manager, I'd say make sure you wear decent boots, clothes you don't mind getting mucky (mud etc will soak through overalls) and a hat.
Your gogglwwes will steam up, most sites use single layer lenses which are cheap, but a bit rubbish. Take them off as sooon as you're back into the Safezone, dry the rubber bits, and use the spray provided (washing up liquid & water usually) to clean the lens. Make sure they are as tight as possible, with the strap running across the 'flat' bit on your crown not the back of your head to get as good a seal as possible around your eyes.
Average spend on paint at my site is £48 for a half day, £80 for a full day. To be brutally honest, take as much cash as you can afford. Paintball games are designed for the customers to use as much paint as possible, since that's where the site makes their money.
Follow the flight of the balls and adjust aim accordingly rather than 'aiming'.
When behind cover, stay a foot or so back, to make it easier to bring your marker to bear.
Be friendly and polite to the marshals, and don't be a prat, they will be much more likely to help you out. Simply ask them how to win that particular game, mose will give good advice, they see the same game run over and over again.
Take great pleasure in shooting the 'Rambo' type who is guaranteed to be there, and remember it's supposed to be a laugh. Don't take it too seriously!
Airsoft is the fiture, my airsoft site, in a WW2 underground bunker, is far busier these days than the paintball site. It's cheaper, not as painful and the games tend to be much more immersive, rather than simple 'capture the flag' affairs.
Oh, for 'modern laserquest', check Warfighters out. Pretty slick operation with an amazing site. (Not as good as mine, of course!)