Firstly don't bring anything you are not prepared to get muddy or dirty. If you are playing in the woods, camouflage is a great idea weatherer it is BDU or hunters camo. If you don't have and don't want to rent camouflage it is suggested you wear earth toned colors so you don't stick out like a sore thumb. Any color is good for indoors.
Your amount of clothing should be what you would wear if it was one season colder. Long paints like jeans or sweatpants are good, and a long-sleeve shirt with a hooded jacket are good even in the summer, because they will absorb paintball impacts. For shoes, boots are the best option, unless you know there is no mud or its mostly open space, then sneakers are fine. Bring thick socks, even in the summer.
A hat is very valuable for absorbing impact, along with gloves and a neck covering. Also many men play with a hard cup and a chest protector is suggested for women.