A good warlock requires good macros. Macros allow you to do things in sequences or do multiple things with one button, the great thing is there completely legal.
A good one start is with your curse's.
/castsequence reset=target Curse of Agony, Immolate, Corruption
This will cast each curse when you click it. The rotation resets when you a) Change target. b) Finish the sequence. c) When the target dies.
Another Warlock Tip