Generally I have my shammies DPS whatever my tank is currently targeting.
I use the same rotation (click castsequence) all the time.

It is:
Flame Shock
Lava Burst
Chain Lightning
Lightning Bolt

Ensure your shaman always have a Water Shield up.
And one of them has Mana Spring Totem down.
You can take the Elemental talent for mana regeneration.
As well as the talent for reduced cost of your spells.

As as your team gears up, mana becomes less of an issue.
Crit is nice, as the next two spells cost 60% the normal mana cost.
And you'll eventually have FS - LvB, which is a guranteed crit early every fight.

With a click macro you can pull spells out of the sequence by moving the macro.
Until you get Lava Burst, you'll not want the macro there.
It doesn't hurt to have it click four buttons, and nothing on button 2.
Similarly, if mana is an issue, you can pull out the 3rd spell too (chain lightning), and go with Flame Shock + Lightning Bolt only.