At low levels, you do not need to worry too much about the stats on your gear. Pick the gear that has your primary stat, and equip any item you come across that has more of that primary stat.
Agility: Feral and Guardian Druid, Hunters, Brewmaster and Windwalker Monk, Rogues, Enhancement Shaman
Strength: Warriors, Protection and Retribution Paladin, Death Knights
Intellect: Mage, Priest, Warlock, Elemental and Restoration Shaman, Balance and Restoration Druid, Holy Paladin, Mistweaver Monk
Additional stats include Critical Strike, Mastery, Stamina, and Versatility. These are not as important as making sure you equip an item with the right primary stat.
The class you choose affects the type of armor that is optimal:
Cloth - Priest, Mage, Warlock
Leather - Rogue, Druid, Monk, Demon Hunter
Mail - Hunter, Shaman
Plate - Warrior, Paladin, Death Knight
Classes can wear armor a tier below their optimal one, but it is considered subpar.