If you need more info about the game (quests, items etc.) check out
http://www.thottbot.com .
Joining a guild usually has it's advantages: people in the same guild are more willing to help out with quests and creation of items.
Accept the role you play in a party based upon your character: a priest/ healing druid keeps partymembers healthy, a warrior tanks etc.
A balanced party has more chance of succes then an unbalanced party with higher lvls (unless were talking about an average +5 lvl).
Always come prepared: if your party goes questing somewhere make sure you have already picked up those quests, if a quest can't be shared you have to do it all over again with another party.
A general rule states that "rolling" for loot means N (Need) goes before G (Greed), weak players that join the group specifically for those items but don't make themselves very usefull to the team are not appreciated.
You can get alot more out of players from the opposing faction than just honorkills: in contested territory they sometimes help eachother out rather than stand in eachothers way (which means both sides spent more time to get their quests done which doesn't help anyone) -> but unfortunately most players just fight, we've had a few naked (means they're much less of a threat, sort of a declaration of coming in peace) people from the opposing faction coming to Orgrimmar just dancing and joking around (also we climbed on the roof of Orgrimmar which, as I heard from other players afterwards, is considered Illegal because it's not supposed to be possible and you can get banned for doing it).
In hostile environment (contested territory or territory from the opposing faction) you should look around you with everything you do.
There are alot of players out there that wanna take you down when your least prepared for it (often they follow or stalk you and wait untill a creature damaged you properly, this gives them an advantage over you, also they team up against single persons or attack you when they have a much higher lvl).
There are many ways to get sneaky kills (example: In Gadgetzan the guards will attack anyone who
starts a fight, unless your a hunter that fakes death and attacks with pet (this not only allows you to fight without the guards attention, but also when your target lashes back the guards attack him/her) or you use the Goblin Dragon Gun which also doesn't trigger the guards).
Proffesions are also important: some allow the creation of items and others allow the gathering of the materials to create items, you can only have two proffesions so it's most efficient to have one that creates items and another that gathers the materials for those items.
Engineering is probably the most expensive proffesion: required materials come mostly from mining, but also skinning/herballism and even alchemy
(alchemists can create Goblin Rocket Fuel used for various engineering items), but the rewards are great (both powerfull items and very funny items like a mechanical squirl Goblin Construction Helmet and Gnomish World Enlarger).
there are three secondary proffesions: first aid, fishing and cooking.
These don't count towards your "two proffesions limit" thus are worth training.
Making smart use of the Auction house enables you to earn alot of money.
There's an auction house in Gadgetzan which can be used by both Alliance and Horde, this is very usefull when you want something that normally only the opposing faction can get ( example: only Alliance can get blue fireworks schematics and only Horde can get red fireworks schematics).
