Arcane Mage
Rotation
Opener: Arcane Intellect out, Arcane Power with Presence of Mind on the pull, then Frostbolt or Fireball as the filler.
Priority: Arcane Missiles only when Clearcasting procs or mana is no object; the filler is Frostbolt (or Fireball) because Arcane Missiles is mana-hungry. Arcane Explosion on packs.
Cooldowns: Arcane Power + Presence of Mind + Pyroblast or a max-rank Frostbolt for burst; Evocation mid-fight.
Forever notes: Arcane is the utility and burst tree; in a raid the damage comes from the other tree you pair it with.
Stats
Spell Hit to 16%, Spell power, Spell Crit (Arcane Instability), Intellect (Arcane Blast scales with it), then Spirit with Arcane Meditation.
Arcane Blast stacking means Intellect pulls double duty here.
Numbers for every spec and a gear comparer: stat weights.
Where it ranks
See the tier lists for PvE and PvP placement, and Classic vs Forever changes for what Blizzard altered in this class.
Wowhead and Icy Veins keep spec guides of their own: Icy Veins Arcane Mage, Wowhead class guides. Our rotation notes are editorial, written for the Nov 2 tuning.