TF2 is very easy to explain :
Don't hang near a enemy pyro.
Kill the medic.
Don't hang near a enemy scout.
If you see a guy just like you with the same name as you, shoot him in the face, that'd be a spy.
Heavy Gun guys are more intimidating than they really, except if they have a medic with them, in that case,
kill the medic.
Destroy turrets when you can.
Demomans are bastards.
Kill the medic.
Snipers are cowardly bastards.
Don't use teleporters if you run fast.
Kill the medic.
And that's pretty much it.
You can play the heavy gun guy while John heals you (in this case,
don't kill the medic) and I'll play another class to help balance the trio. (example : Soldier, to have mid-range/long-range firepower)
And remember :
(not IN the thread because of bad words)
http://www.penny-arcade.com/images/2007/20070921.jpg