Left 4 Dead 2

Here are some tips and strategies you should consider when playing as the Survivors. Some may seem obvious, some not.

Have your team on the same page on which Infected to clear first.
For example: Jockey, Hunter, Charger, Smoker, etc. When your team mates know what priorities to follow you will find clearing to be much simpler.

What is clearing? Clearing refers to shooting off a special infected who has somebody pounced/pinned.

Make tanks fight where you are comfortable.
A tank player can be good, but ultimately they can be only as good as their support. When applicable, get your team to a position to ward off any SI attacks and fight the tank where you can have the upper hand.

Make speed and distance your goal.
In the first game it was important to only use your health packs and pills when you found more or if you were desperate. On this game I tend to suggest using at least your pills any time you or your team is moving slowly. The quicker your pace the more distance you cover and less attacks the enemy will get.

Go into rooms cautiously.
I can’t tell you how many times my team has successfully launched an attack and downed all four survivors because they unwittingly entered a room small enough for Spitter goo to cover the entire floor thus dispatching them. Go in as pairs or at least leave one lookout survivor.

Communicate and work as a team.
This is above all the most important rule. Call out Infected as you see or hear them. Call out where you’re pinned or pulled. Call out items as you see them. If you are moving slow let your team know. Communication and teamwork is the most important attribute of a team that is successful at this game.

source