Alright, some of these points might have been made above but I can't be bothered to pick and choose them.
- MEELEEEEEEE, i think it's one of the most powerful tools in the game. it causes NO friendly fire damage. you can melee out of almost any situation without causing any damage to your team. hunter on survivor - melee, hunter jumping at survivor - melee, smoker got you - melee. boomers will go back surprisingly far if you melee them, so long as no-one shoots them in the mean time!
- A good tip with a horde in close combat situations is for the person at the front to crouch and just constantly melee and have the rest of your team behind you shooting them as you knock them back. works especially well in corridors and trains and stuff...
- molotov flames spread. yes, a tank may be coming, yes you may hit the tank with the flames and make a nice firework display. but if your survivor gets knocked down onto the floor and yeah...much burning & death. burning....and death.
- statistically you are MUCH less likely to cause team damage with the hunting rifle / assault rifle. you have to think about aim more, especially in panicky situations like a hunter attack.
- i've also noticed that you can still reload whilst meleeing, so if you run outta bullets hit the reload key then melee away!
- said before - but if at the front, crouch so we can shoot over you
- stay together, this means 2 things - a) dont run off and b) go back for stragglers
- do not activate any switches, fuel pumps, bridges, cranes etc. UNTIL THE WHOLE TEAM IS READY. people might be low on ammo, fighting hordes, low health, placing explosives and would like a few seconds to recover / regain their sanity before continuing.
- the explosive gas canisters and petrol cans are put there for a reason - use them

- if you're going to use pills, think "does anyone else need them more"
- if you're going to use a healthpack, think "does anyone else need them more"
- they put 4 healthpacks in the safe room for a reason, it means there is one each. don't steal other people's healthpacks or maybe they'll be less likely to save you from a horde/tank/witch. >.<