I have one key that I use for DPS. I have one fire mage and two elemental shamans.

The macro for my fire mage:

/target [target=target, harm, nodead][target=focus-target, harm, nodead]
/use 13
/use 14
/cast Combustion
/castsequence reset=target Living Bomb, Fireball, Fireball, Fireball, Fireball, Fireball, Fireball, Fireball

The macro for my elemental shamans:

/target [target=target, harm, nodead][target=focus-target, harm, nodead]
/cast elemental mastery
/castrandom Lightning Bolt, Lightning Bolt, Lava Burst, Flame Shock

(reference )

Also, if hotstreak procs on my mage, I have another macro (another key) to immediately cast pyroblast.

/target [target=target, harm, nodead][target=focus-target, harm, nodead]
/stopcasting
/cast Pyroblast

And I have an AOE key as well for my mage:

/castsequence reset=30 Blast Wave, Frost Nova, Dragon's Breath, Cone of Cold, Arcane Explosion, Arcane Explosion, Arcane Explosion, Arcane Explosion, Arcane Explosion, Arcane Explosion, Arcane Explosion, Arcane Explosion


Hope that helps; you need to experiment and find out what works for you...