wear a cup when possible. and a thick shirt, unless you like welts on your torso.
I never wore a cup.
I used to play in the woods, then too much speedball started to happen. I go back as far as oil based paintballs and no pump handles on the nelsons.
I still have several custom pumps.
Wear a top coat, not tucked in, it will catch the distant shots from the nubs and drop to the ground. Keep your pods under the coat if they're clear. We used to call those guys with clear tubes, electric lizards.
Don't pick up the spilled paint off the ground.
Wear a bandana.
Wear kneepads. Nothing hurts more than a sharp rock.
Pay attention when you're reloading and make sure the hopper lid is closed.
Keep your situational awarness high. I used to sprint the wire and get inside the base edges, then turn around and let the opposing side join me, shoot them all in the back because they weren't paying attention.
Favorite trick of mine was to shoot at them, tell them to check themselves, they stop shooting back, while checking you pop them again.
If you're going to play arena or speed, keep low, shoot and move. If it's indoor ball, and astroturf, use the knee pads to slide in to the bunkers then shoot over the top.
Don't hyperventilate in the mask, don't lift up your mask. If it fogs, get behind a solid object and pump your mask in and out. Do not take it off.
There's more, but it's your first time... have fun. Don't drink booze.