Goof off on something until you get an idea for how things play.
Here is my impression on the collective areas of WoW:
RacesThe Night Elves are my favorite race to start as. Teldrassil is one of the most beautiful places in the game, with some of the best music to go with it. However, Darkshore (the NE second level area) is pretty lame, and Ashenvale (the third area for the Elves) is always being attacked on PvP servers with lots of Horde. Something about Astranaar (the Alliance town there) makes it easy to own.
The Orcs and Trolls have the second-best (IMO) starting spot in the game. Durotar might be somewhat barren in terms of vegetation, and maybe it's just because I played as an Orc Warlock for so long in beta, but I like that starting location. The Barrens is a very fun and a very versatile area to play too, and in general,Kalimdor is a very worthwhile place to play. Thousand Needles doesn't have much Alliance, and neither do the Stonetalon Mountains despite the Alliance flightpath. That makes central Kalimdor fairly easy to work through as a Horde player. In general, I prefer the traditional Orc over the Troll.
I can't stand playing as Tauren. They're so big. And clunky. And fat. They just feel slow. But, the Tauren starting area, Mulgore, is right next to the Barrens, so you can go to do Barrens quests at the same time as Orc and Troll players. If you don't mind being a cow, then maybe it'll be worthwhile.
Humans also have their own starting area. It's populated fairly well (Elwynn Forest). Having said that, the second levelling area you go to, Westfall, sucks balls. Maybe it's changed in retail, but I remember having to struggle through it. Beyond that, though, it's fun -- and personally, I'd take my Night Elf or other Alliance character there to level. Redridge Mountains is a good area, and so is Duskwood. Duskwood leads directly to Stranglethorn Vale.
Dwarves and Gnomes -- well... I hate Gnomes. They're just... annoying. I emote punt them every time I see one. Dwarves are okay, and while I haven't ever spent the time getting through their starting areas, it seems like they're fairly well-done (Loch Modan and Wetlands are populated with creates fairly well; I don't know what kinds of quests are there).
Then we come to the Undead. I've tried three times to start playing the Undead, and I just can't get into the spirit. Maybe it's that the area is so dark or something. It seems to me that the Undead are not all they're cracked up to be; in the first zone where you start out, the Undead are given a much more human quality than any other race is. It just doesn't fit. Plus, you have to work much harder for reputation with the other horde races. The third undead zone, Hillsbrad Foothills, is a hotly contested territory on PvP servers.
After the first three major zones, sometimes four, you really start sharing zones with other races, so it doesn't matter so much.
ClassesWarrior: what Blizzard has continually stressed as the "not-major-damage-dealer-more-focusing-on-tanking-ability" class dominates PvP. As a rogue, I've been 3-shotted by warriors multiple times; I wear two levels of armor below them, and since they traditionally have much more health than I do because of different stat builds, rogues, the most powerful PvE class in the game in terms of melee damage, get our asses handed to us. Warriors also have an ability that seems to be specifically geared towards rogues: (IIRC it's called) Retaliatory Strike. Rogues have an ability to increase their dodge chance by 50% for 15 seconds, and another (if you're specc'd right) 15% for 5 seconds; I've had up to a 90% dodge rate. Retaliatory Strike adds an immediate, undodgeable, unparryable, unblockable attack immediately after any dodge.
Rogue: Typically, if a rogue gets the jump on you, you're toast. With stun-locking abilities such as Cheap Shot, Kidney Shot, Gouge, and if you're an engineer, bombs, they're fairly good contributors to PvP. They are also the single most powerful PvE melee class in the game in terms of damage. Because they're melee, however, they can often only handle one to two enemies at a time. Plus, they have the ability to walk around stealthed. Specc'd properly, rogues can be especially powerful at either PvE or PvP.
Mage: Frail, but packs a wallup. Magi have incredible direct damage and area of effect spells. They can also get out of any stun effect in the game (with the exception of Sap, which is negated as soon as any damage lands) every so often with the use of the Blink teleportation spell. Mages are one of the best crowd control classes in the game, and are extremely effective at protecting themselves.
Warlock: One of the more robust and still difficult classes to play, the Warlock is fun. Generally as frail as a mage, the Warlock controls demons as pets to do their bidding. Manipulating fire and shadow to their will, Warlocks are proficient at causing damage over time, interfering with casters (the Curse of Tongues, which causes casting time to increase quite a bit). They also have a good Crowd Control ability with their succubus pet to keep you "seduced" (apparently my female rogue is a lesbian) while they run away to get range on you. The warlocks are great at crowd control, and a good warlock is also good at tapping everything around him with damage over time.
Priest: Being a healer may sound like a boring job, but it guarantees that you'll always get a group. Good healers -- the ones who watch players and their pets -- will always have room. Having said so, priests are also amazing in PvP. A shadow-specialized priest has debuffs that cause massive damage over time, and they also often have psychic scream, which makes you run away with nothing to do about it. Priests are much more versatile than they might otherwise seem.
Paladin: Stfu noob. Paladins have a bad reputation because they have "the bubble" -- the immunity shield that lets them heal themselves and resume fighting once it's back down. Disadvantage: absolutely no ranged weapons, and they're limited on the amount of damage they can do. They're a fair tank and a fair healer, but not really great at either.
Shaman: Shaman are really fun to play. They have a wide variety of skills to choose from, and their abilities make them a difficult foe to contend against in PvP and PvE. Shaman can be powerful melee fighters with a weapon buff and low-cost totems, and can also be effective long-range fighters with magic. They also avoid downtime with healing spells for themselves.
Druid: An extremely varied class, druids are masters of the lore of the earth. They can take many forms, which make them effective damage dealers or tanks, depending on their form. When in their normal humanoid form, they also make effective healers and crowd-controllers. When outside of their normal form, druids -- when in bear form, for example, have abilities that parallel that of a Warrior; and when in cat form, have abilities that parallel that of a rogue.
Hunter: The ranged damage dealer of the game. With the ability to have a pet for extra damage, to lay traps for damage or crowd control, area of effect spells like volley, stings that cause damage or hindering effects over time, aspects that buff the player or the group, a mark that increases ranged attack power by quite a bit for anything attacking a specific target, and a wide variety of other tools, the hunter is the most versatile ranged attacker.
ServersPvE - Standing for Player versus Environment, if you want to battle other players, you have to seek out areas to do so.
PvP - Player versus Player. Zones have different kinds of denotations; some are Horde territory or Alliance territory, but most zones are Contested Territory. Any player can attack any other player of the opposing faction in Contested Territory. In factional territory, only that faction may attack first, unless a player of that faction is marked for PvP (either because they just left Contested Territory, or they entered the /pvp command).
RP - Role-playing. You seek out other people and create "stories" to go along with your quests.
RP-PvP - combine Role-playing and Player-versus-Player mechanics.
I am a Night Elf Rogue, Diaris, on the PvP server Illidan. 60 with epic mount woot woot!