Paintball is a rather unique sport and the tactical warfare you engage in is different from anything else. Paintballs don't travel far (~60 yards), they don’t go through things, and they are known to curve. There is a definite skill to playing paintball that is difficult to learn. The most helpful thing someone could provide initially is a list of what not to do, or rookie mistakes.

Top 10 Rookie Mistakes

1: Lifting up your mask
The best way to hurt yourself in paintball is to take a paintball in the eye. This will most likely completely destroy your eyeball so avoid it at all costs by never removing your paintball mask while playing paintball.
2: Staying too far back
If you put a team of moderately experienced players up against a bunch of newbies, the experienced team would overwhelm the other team by pushing them all the way back. Paintball is an aggressive sport and you have to act accordingly. The most annoying thing to see is a player about 50 yards farther back than he has to be. If you are too far back you cannot help your teammates, attack the enemy, or get toward the flag. Of course you don't want to push up too much all by yourself, and staying back is perfectly fine for defense, but you have to take risks.
3: Not using the angle
You will frequently see two or three players all hunkered down in a single bunker. This is very bad, because they all have the same shot on any person and if one person gets a shot at one of them, he has the shot at all of them. You want to spread out so that you can be able to shoot at someone from multiple angles. The best thing to do with someone who has a great bunker is to move around to the side of them, where their bunker won't protect them anymore. This is what distinguishes good players from bad ones.
4: Shooting too much/Shooting too little
You will sometimes see a player who seems afraid to use their gun. It’s a freaking weapon, you have to pull the trigger for anything to happen. More often you will see beginners shooting at things that are way too far away. You should avoid this if at all possible because it wastes paint and gives away your position. One of the most fun things to do is to hide is some bush or behind some tree and wait for someone to walk really close, and then shoot them :)
5: Shooting inaccurately
You must AIM your gun. Sight your gun down the barrel by bringing the gun close to your face and look down the barrel as you shoot. Don't shoot from your hip or hold the gun way out in front of you. Sometimes you may have to angle the gun up a little to get the range you need, but if you have to angle it up too much, you are shooting too far.
6: Not using your cover
Know what protection your bunker provides. If its a small tree, you better be a skinny kid standing sideways. Thick brush will stop any paintball. Wooden bunkers frequently have little holes in them where you can get hit by an unlucky ball. Most importantly make sure that your foot, head, or gun is not sticking out the side. That’s how most rookies get shot. Also when shooting DO NOT shoot by looking over the top of a short bunker. Take quick short looks out the side and when you look have your gun up and ready to pop a cap in whomever should be lurking around. If someone is keeping you down by continually firing on you, take quick looks from a different spot each time and call for help.
7: Calling yourself out too soon
Many times paintballs will hit a particular fleshy part of your body and it will bounce without breaking. It doesn't count if it bounces, it only counts if it breaks and leaves paint on you, hence the name Paintball. There are usually field judges that can tell you if a ball broke and left paint on your back. Likewise, less-than fair players will frequently assume it was a bounce, so have a judge go over and check him/her out.
8: Not communicating or using your teammates
If you’re hiding or trying not to give away your spot, then don't talk. However if the enemy is shooting at you then they know where you are, so talk to your teammates. Point out where the enemy is. Tell people to give you cover, or pin down a guy so you can move. Tell someone if they have a shot on a guy. Ask someone to move up and help you. These are all things that tournament level teams have down pat.
9: Tunnel Vision
A newbie will frequently see an enemy and focus on that person and ignore everything else. Make sure you look around the field, especially to the sides to see if you have a good shot on someone across the field. Do not focus on one guy and forget about all those other people with guns.
10: Shooting your teammates
Teammates are your friends, don't shoot them. This one is kind of obvious but it happens a lot. If someone is bringing back your flag in capture the flag, don't shoot them. Make sure you know who you're shooting at.
Well that’s all for the rookie mistakes. If you avoid all of these, your well on your way to becoming a great player.