One of the most important things to do is to check out the fields where you intend to play. Ask questions, and insist on answers. If you are on your own and don't have a buddy to take you under his wing, ask if the field has games for just rookies or players using strictly rental paintguns. This helps because you will probably be playing against other new players of roughly your own experience level. By talking to a field operator or some of the players that frequent a particular field you will find out what the general policy is toward rookies.
When you have found a field that you feel will help you have a good game experience, the next step is to think about equipment. Ask if you can rent camouflage clothes, or if you need your own. Camos help you last longer by letting you hide better. It can also give you more confidence because you at least like like a regular player. Footwear is a personal consideration, but you need something that will give good ankle support and protection from thorns, rocks, and stickers. They must be comfortable enough to do a lot of running. Take time to break in new shoes since blisters can ruin your day. Army boots in the regular or jungle styles are popular and reasonable in price. Be aware that running shoes do not give adequate support for your ankles when you are running over rocks, fallen trees, and heavy brush.
If you have knee pads, wear them. They make life so much easier when you're kneeling in goat head stickers or sandburs. Some players that like to do a lot of crawling through the brush, also like elbow pads. If you have an athletic cup it is a good idea to wear it. Women players need chest protectors, they are not expensive. Also, I have found that gloves are a real help. They help take the sting out of hand hits and help you stay camouflaged.
Next, check to see what the field offers in the way of face protection and goggles. All fields should have some kind of approved eye wear for you to use, if they don't, DO NOT PLAY THERE! If you are serious about trying the game and they don't have some good head protection to rent, ensure your fun, spend some bucks and buy some. Try them on, especially if you wear glasses because not all eye or face protectors will fit with glasses. The first piece of equipment you should buy is not a paintgun but proper head gear. Try to buy a squeegee as soon as possible. Then you can clean out your own gun on the field. This will ensure continued accurate shots.
If you are renting, go to the field early enough to check in and get all your equipment. You'll need additional time to try out your gun and get used to it. Make sure they show you how to load the CO2, the paintballs and how to tell if the safety is on and how to disengage it. Take the paintgun to the designated target area and shoot ten paintballs at a slow pace while aiming carefully. This allows you to see where the paintgun is shooting and allows you to get used to feel of the cocking motion. Then fire ten more paintball. Aim the first five and shoot as fast as you can. This will show you how fast you can shoot, and if you are going to have problems with double feeding or pinching balls. Change the CO2 before you leave the target area so you'll have practice loading and unloading it and to make sure there's a full charge for the first game. Be sure you clean your gun before the game starts and remember to put a full load of paintballs in.
Most fields have an orientation meeting before the first game to explain field rules and select teams. Do not be afraid to ask questions if you don't understand. Be sure to find out what the local custom is on how you call yourself out and how to call for a paintcheck.
After you have been assigned to a team for the game, let the team captain or the other players know that you are a new player and will take suggestions and work with the team. If they know you want to learn or that you will work with them things will go better. Buddy up with at least one other player so you can cover each other while changing CO2 or loading paintballs. Take a tip from veteran players, load anytime you have a chance just to keep you weapon as full as possible. If you feel you have time and there is any doubt about the amount of CO2 you have, change it. Try to carry more paint and CO2 than you will need so you don't run out during a fire-fight.
Try to avoid typical rookie mistakes. When moving through open ground with no cover, have someone on your team give you cover fire. Move quickly, and never stop in the open. Try to run a zig-zag pattern. Scan ahead for suitable cover that will hide your whole body. When you get good cover, look around, and when you are prepared to give cover fire, have your teammates advance in leap-frog fashion. Rookies usually stay in one place too long. If you stay put too long, the other team will find you and shoot you. Do not let your fear of being shot for the first time make you play too cautiously. If you have a fear of being shot, you need to force yourself to be aggressive. Usually after the first couple of times the fear of getting hit leaves you. Another good habit to develop is to check behind your back every so often. It will prevent your getting shot in the back and allows you to keep tabs on your teammates' locations.
After the first couple of games you will get to know some of the better players on your team. You can learn a lot by watching them play. Ask them questions between games because most will be glad to give you reasons why they do certain things. Use what you feel will work for you and forget the rest.
These guidelines will give you a considerable edge on most new players and even some experienced players. Don't forget you are playing paintball to have some adventure and fun. Keep your sense of humor, expect to be shot some and have a great time!