Which class should I play? Tanks try to attract the attention of the monsters and can take quite a beating. Healers can heal, duh. Pure DPS is a damage dealer. They may not be able to take a beating, but hopefully they can kill faster than being killed.
Tanks - Death Knight, Druid, Paladin, Warrior
Healers - Druid, Paladin, Priest, Shaman
Pure DPS - Hunter, Mage, Rogue, Warlock
All classes have the ability to be dps. Ranged stand at the back and shoot or cast at the monsters. Melee get up in the fray and stab, whack, bam.
Ranged - Druid, Hunter, Mage, Priest, Shaman, Warlock
Melee - Death Knight, Druid, Paladin, Rogue, Shaman, Warrior
Each class has a preferred armor class. Cloth wearers are the squishiest, with Plate wearers having the strongest armor (and consequently the higher repair bills).
Cloth - Mage, Priest, Warlock
Leather - Druid, Rogue
Mail - Hunter, Shaman
Plate - Death Knight, Paladin, Warrior
How do you choose which race?
First you must ask, which Faction. Then you must see which races can be your chosen class. Then, you could play around with Min/Maxing and choose based on racial attributes (you're better off going to Elitist Jerks for this information). Or you could be like me and choose by looks or role-play-ability.
Racial Bonuses to Professions may also make a difference to you.
AllianceDraenei - Jewelcrafting
Dwarf - Archaeology
Gnome - Engineering
Worgen - Skinning
HordeBlood Elf - Enchanting
Goblin - Alchemy
Tauren - Herbalism
Which professions should I have? Gathering professions are just that, professions that consist of simply gathering things. Production professions rely on gathering to craft different items.
Gathering - Herbalism, Mining, Skinning
Production - Alchemy, Blacksmithing, Enchanting, Engineering, Inscription, Jewelcrafting, Leatherworking, Tailoring
Well matched pairs:
Mining/Blacksmithing - ideal for plate wearer
Skinning/Leatherworking - ideal for leather or mail wearer
Enchanting/Tailoring - ideal for cloth wearer
In the end, play what you enjoy. I encourage all of those new to the game to try out every combination that appeals to you, but then you might wind up an altoholic like me. This "guide" was written purely as an aid to myself in making choices. I post it here in the event that it may help others.