STRATEGY Starting off we can look at the stages of the game and what happens in each.
The Break: Start all players at the start box so that no one running will cross any shooting paths, give priority to your front players, and tend to put anyone who will be burning off the break towards the middle. All players should know exactly what path they will be taking while running/diving towards their first bunker and they should also have a general idea of their 2nd/3rd/4th positions will be as they move down the field.
As soon as the game begins, you can do one of three things. "Delay and Burn" consists of bringing your gun to bear on a lane that an opponent will run through and putting as much paint as possible down that lane. After about 5 seconds you will then move to your first bunker. This is typically done by players who will be playing towards the back center of your side. "Run and Gun" consists of running to your bunker while shooting a lane. This is usually done by Backs and Mids who don't have to move through hot lanes. The third option is your "Run off the break." This is what your front players will be doing, as they have the hardest and most vulnerable runs most of the time. Other teammates who have to run through very large open lanes to get to their position also use this.
Early Game: You've made it to your first position, now you need to do a couple things. First off, start communicating with your team. Call out eliminations and opponent positions. Listen for the same from teammates. If you've lost a teammate who was playing a key bunker, call to your backs/mids for someone to fill it ASAP. Figure out if your next couple of bunker choices will be affected. Back players: you want to take control of your lanes and keep your opponents from doing the same as much as possible. If you have control of a lane, use that opportunity to move teammates/yourself down the field. If you don't have control, get it, through snap shooting and teammate assistance. Be aware of the field, don't zone in so hard you don't know that your snake side teammates have all been eliminated. Watch both sides of your bunker. Front players, look for your Backs to get control of your lane for an early opportunity to move up. If not, look for good shots to take/help your back with the lane. Mids, fill where/when needed, communicate constantly, keep the enemy team out of key bunkers as much as possible.
The Midgame: If your team made it out of the break/early game while maintaining an even or higher number of players, this is where you get aggressive. Backs, you're then one pushing your Front player up the field, do so aggressively. Call out where the opponents are shooting, tell your Front players to push if you see an opening. Mids, look for opportunities to fill positions on the opponents weak side and help clear that side. Move. Fronts, listen for your backs to call for moves. He says move, you'd better already be moving. Shoot across the field, call out opponents. IF you're up on players, look for moments to bunker opponents and or trade (both players hit each other at the same time, ref pulls both.)
If your team goes into the midgame at a player disadvantage, play defensively until you can even it up. Cross it up and prevent opponents from moving into key positions. Controlling key areas can lock down all enemy movement. Front players if you're still alive, you're the gamechanger here. Look for safe bumps when possible, but don't take risks. Be good at gun battles. Try not to trade as that increases the other teams advantage.
Late Game This is the part of the game where your team has a large advantage, and is just looking for any small opening to push all of the way down the field. As a Front/Snake player myself, I'm always staying aware of what is going on down the tapeside (sideline). If snake side is 2v2, my movements down the field are going to be limited. But if it drops to a single opponent Back player suddenly more opportunities open up. All it takes is one snapshot to put him in his bunker and suddenly I'm already at the next knuckle of the snake. If there is no one at all locking me down, I can push all the way down the snake til I'm at their 30 and pinching (firing paint from two different angles with a teammates help at a bunker such that the player behind it doesn't actually have the angle to take cover) every player on their team so hard that it's impossible for them to avoid all the paint. (One of the many reasons why it is incredibly important to fill certain bunkers if a player is lost.) Focusing on opportunities like that is something that should be done all game, but occurs more frequently in the late game. Find the blind spots, have the players who aren't under fire move up, call out when their last opponent/s is looking at you so your teammate on the other side of the field can move up unscathed. Run a train down a weak side with a large player advantage (multiple players running down consecutively bunkering the last remaining opponent/s.) There are many many ways to close out a game, these are just a couple. Once you eliminate the last player, grab the flag and tag your start box for your points :)
COMMUNICATION This is a big one in paintball. When I first started playing for a team, one of the first things we had drilled into us was that we had better be doing one of three things at all times:
MOVE SHOOT TALK - MOVE SHOOT TALK - MOVE SHOOT TALK
If we weren't doing one of these three, we were useless to our team. Now, you can have 5 opponents throwing paint at you, preventing you from shooting or moving, but you can ALWAYS communicate with your teammates. You should have a naming system for all bunkers/positions on the field, calls for kills and losses, calls for opponent positions, calls for preplanned movements down the field. Call when you have an opportunity to move, when you're filling a position, or when you lose a teammate. Call which side an opponent is shooting out of, if he's on you or not. If you've got multiple opponents putting paint on you, call out how many and which positions. Communicating as much as possible in an efficient manner is one of the biggest factors in leading a team to victory.
MOVEMENT I'm going to throw the concept of "walking the field" under movement, though it is a huge part of strategy and planning. Walking the field gives you a ton of important information. First of all, you get to know the layout and intricacies of each field. While walking the field you should be keeping in mind a couple of things. Which bunkers can lock down movement the best? Which bunkers provide the best support for the positions the team is playing? Where are the blind spots that we need to be careful of? Which bunkers are key to hold, and which bunkers allow the most offensive pressure? Everyone on the team should know the shots that each position has so they know where a teammate can shoot. Plan out multiple opens, from aggressive breakouts that put 4 teammates at the 50, to conservative openings that have everyone burning off the break minus one or two teammates. You want to know the exact route to make a bunker down to the footsteps and exact point you dive/slide. Look for vulnerable points where you can get hit and avoid them. Many times, you can dive 10 feet behind a bunker to avoid paint, and slide right in no problem once you pass the danger zone. Movement in paintball is far beyond the scope of writing unfortunately, the only real way to get better is to PRACTICE! Practice proper diving and sliding technique, wear the proper equipment, CARDIO, and STRETCHING.
GUN SKILLS Shooting drills: There are tons of videos of pros running drills, look them up and practice. These are some commonly used drills.
"Off the break" - Silently counted start, sprint and slide/dive to bunker. Practice reaction time and proper form.
"Run and Gun" - 1 player runs down a preset path on the field, shooting at multiple targets set up. Many variations: targets on one side of the player; on both sides to force hand swapping; weave in and out of bunkers
"Burn the Lane" - Start at start box, count a start silently, bring your gun down and burn a target set up at the other end of the field. Set a time limit mentally and restart once you hit it(5 secs or so), practice this until you can confidently burn a target off the break.
"1v1" - 2 players starting, 1 at each start box. Free movement.
"Snap Shooting" - 1 player in each of two bunkers, gun battling. Typically one shot, check into the bunker before you shoot again.
"Cross Up" - 2 players cross up defensively; 3+ players attempt to break it.
"Gatekeeper" - 1 player in a bunker, no movement allowed; 1-3 players must pass/eliminate him.
"Killbox" - Stand the width of the field apart in an open area - nothing blocking your view of each other. On a count, start shooting at each other. You may move in a 3x3x3 box to avoid paint. First person to get hit, call yourself out. This will highly improve your ability to see paint, dodge paint, and increase accuracy of that first shot. The first shot is highly important as it forces the other person to move, hurting their own accuracy.
"Catfish" Play the snake half of the field, 3v3. Put one back center, one snake entry, one snake corner. The object is to get a person to the snake50 and have him hold for 10 seconds. This will be a large gunfighting and communication game. Your team will work together to move your snake player up. This is a very important skill to have.
"ABCs" - Play a normal game, or a game of catfish, and on top of normal calls, you call out the alphabet to each other. Starting on one side of the field, call A. The next person calls B, then C, and so on. Once you hit the end of the field go back the other way. This will improve communication.
1v2s/2v3s/etc anything uneven is good practice