-nmo_ are objective maps, nms_ are survival maps. There's been an explosion of new/beta maps that really need some work. If you want to see the best maps this game has to offer, I recommend: nmo_chinatown, nmo_broadway, nms_flooded, nms_isolated, nms_northway.
-On survival maps there are medical crates, FEMA supply bags, and supply crate drops. Hit "c" for compass to see where the "Zones" you have to defend are. The medical crates can be placed (if there's no items on the ground nearby) in the ghosted spots nearby at most zones. Zombies move to attack you and flood the zones. If there's no player to attack, they will smash up the zone. Once all "zones" have reached 0% health, the national guard considers your portion of the redeker plan a lost cause and you lose. FEMA supply bags are found in wooden crates (3 bags per crate) and heal 10% zone health each. Merely drop them in a zone and they disappear. Don't waste them, stack them outside a zone. Supply drops come every 4-5 rounds or so, but you can call them manually on some survival maps with the flaregun. IF and ONLY IF the old crate is empty/gone, when you shoot a flaregun straight up a supply chopper should arrive and drop a supply crate where you signaled.
-COOPERATE. Lots of newbies can't handle that for some reason. You'll be hard pressed to solo the game.
-20 kills gets you a free re-spawn within the round on survival. Lots of newbies can't manage that.
-Grey vision means low health (like 1 smack and you are dead), and veins at the edge of your vision means you are infected and turning.
-Pills are a temporary cure.
-On rare occasion, a wound might bleed you to death unless you use bandages. You'll constantly take damage and audibly wince.
-Zombies that don't fall from a lack of brains may stand up again. I've seen people turn, then get grabbed by the zombie they just knocked down.
-In 1.06 friendly fire is OFF by default (With the exception of killing infected players) however many servers still have friendly fire on. Few servers advertise the FF status, so be careful. This game is hell with a single troll (though they always bring friends) with FF on. I recommend the DeadByDawn servers, but that's just because of ping.
-With FF off, you can still be killed by other players if you are infected. Some people are asses and will pump shotgun shells in your face if they see you get scratched. They're either idiots or trolls. Give the infected guy a top-tier melee weapon and let him get the 20 kills for a free respawn. If they request to be killed, oblige BEFORE the round ends so they respawn for the next.
-If someone is trolling by means besides teamkilling. Things like staying behind in an invincible spot on a survival map, such that everyone dies but he prevents a new round from starting. They've fixed/removed most such spots, and I haven't seen that since 1.04. Just in case however, know how the ban system works.