1, Attack together for maximum damage. Only attack alone for tactical seperation, or tactical delay. But that's harder so only go for that if you think you are up for it. If you miss an attack, try and save or despawn your infected by running back through the map until you're promted to despawn.
2. Die together. That will mean you spawn together and can get as many hits in as you possibly can. Don't save a Special Infected who is nearly dead for the next attack, try and get killed off so you're fresh for the next chance. SI are really weak health wise.
3. Stay alive as long as possible as Tank. Keep your distance and throw rocks rather than head in without support. The longer the Tank is alive, the more hits and damage your fellow SI can do. Block the Survivors path if playing on vanilla (normal servers), to prevent Survivors from outrunning you.
4. Only go in with support as Tank - The Tank is both slow and weak, especially if Survivors are carrying automatics. Only go in with support of your fellow SI, and only try and run/punch Survivors who are below-green-heatlh. Green Survivors will always outrun you, unless they get stuck on something. As they shoot you you also get a slowdown effect, so you're even slower if they do that.
5. Always save the Spitter for an incap. Don't be tempted to spit unless you're certain a Survivor will stay in the spot you spit for some time. Otherwise they'll just run through the spit and take little to no damage. If you however spit on someone caught in Commons after a boom, or even better, caught under a Hunter, Charger or Smoker, you'll rack up damage points fast.
6. Waste the Spitter in Tank fights. The Spitter is great but you rather have other SI in Tank fights so you get incaps. The Boomer is nice during Tank fights though as it slows down and disrupts Survivors for the Tank and the other SIs to get hits in.
7. Try and get as many attacks in as possible. Don't worry so much about specific good points to attack, but rather try and attack as many times as possible in a match to wear the Survivors down. Once you gain more knowledge of the game, tactics and maps you can worry about specific attacks at specific points.

1. Stay together. If you go off alone, you'll get picked off alone most likely. Make it your mission to keep track of where everyone else is, and to clear them of danger as soon as possible. If you all do that for each other, you're halfway home.
2. Don't stay too close together. If you're all lined up you all risk getting charged, boomed, spat on or rocked, tree-trunked or car-ed together though, so try to not be a single target together, if possible.
3.Clear the Commons. It only takes one single Common to frick up your aim and ruin the day. As you head into each new area, try and clear out all the Commons for the incoming SI and/or Tank attacks. Pro gamers always clear out constantly. If you're not out of ammo by the next ammo pile, you have done something wrong.
4.Don't worry about friendly fire. Your team mates will much rather have a few damage points from you, as you clear them of a horde or SI than the horde or SI themselves. VS is not Expert Difficulty, so the damage the infected do compared to your team mates, is not comparible.
5. Keep moving even when boomed. It's easy to just stop and stay still when boomed and blinded, but try and keep moving and be a harder target to hit. Meleé and shoot your way forward. Again don't worry so much about friendly fire.
6.Shoot. The. Tank. When the Tank spawns, and you get a view of him, keep firing. He's not gonna kill himself, and the faster you get rid of him the better. He's slow, and he's weak. If 4 Survivors all shoot continously at a Tank he's down in seconds. Priority should be the Tank, and once he's downed, you can worry about picking others up or killing off the lingering enemies.
7. Only pick up one Survivor at a time. If more of you are downed, concentrate on one at a time. Have a friend cover you as you pick up, don't go picking up at the same time and have no cover whatsoever. If 3 are downed and you're the last one standing, make sure you kill of everything before starting pick ups, and don't be afraid to let go to go kill and then come back to pick up. Also, if one of the downed Team Mates have a Magnum, stay close to that person, because he/she/it can clear infected off easily with the powerful Magnum. Try and go for the lowest of health first though, and don't worry so much about the ones with lots of down health still. Unless you're very split up, then just go for the nearest one for best chance of survival.
8. Use medkit when you have plenty of time, only use temporary health when you're short on time. Temp health is just that. Only pop pills or adrenaline for tactical reasons. If all infected are killed and you have a moment, always use the medkit and save the temp health for an emergency, or at a point when you need to get someone up quickly with adrenaline. In an emergency you will often not have the time for healing with a medkit. You'll just risk dying with one unused on you.
9. Know when to leave Team Mates. If you're close to the Safe Room and everyone else is downed, you may consider running there for points instead of fatality try and get your mates up. If the infected are on your mates, they're not on you, and sometimes a short section of distance points make the difference between winning and loosing.
10. Move. Fast. Don't spend time looking for stuff and lingering, giving the SI time to attack your team again and again. If you skip all the shopping and keep moving, they will have a hard time keeping up and getting attacks in, and you'll progress faster=more points. However, if one of you is slow from damage or by gameplay choice, you all have to adapt to the slowest in your team. If one is hurt, keep that person in the middle of the group, rather than at the back where he/she/it is an easy target.

Have a good time! It's a game, and a fun one at that! Some things are down to pure luck, or unluck, depending on spawns, lag issues, spit spread, amount of commons and AI's sometimes unpredictable behaviour etc! Be nice and supportive of each other. No one is here to have a bad time, eh? And also, don't be a poor loser or a rage quitter. That's sooo 2010.