General:
1. Work as one, never blame your teammates for your lost , is a team game.
2. Always try to stay positive.
Survivors:
1.Try to buy a laser as soon as you get the money, it works well with almost any gun (except shotgun).
2. With shotguns or snipers, after you shot, hit mouse 2. It will speed up the recharging time.
3. If you're new or not that good, stay in front or in the middle of the team, the best players always need to stay behind.
4. Even if you're in front or middle, always look behind. Someone may get hunted or smoked.
5. Learn every infected sound. Is not that hard (edited)
6. Learn every infected height. I know it sound a little weird, but it will be easier to headshot them. At begin, you will fail a lot, but with time, you can be a pro. (just like me ) (edited)
Infected:
1. As a spitter, suicide after you spit.
2. You can rocket-spawn. You walk, press "R" and mouse 1 ( default spawn button) and you will respawn mid air, rocketing.
3. Try to set up a charger/hunter/smoker attack with a spit
4. When someone gets tank, try to hit the trash can or the car. It deal massive damage and incapacitate in 1 shot.
5. When someone is tank, spam the boomers.
I will probably post more, all I could think now.