Its not an easy fight at those levels. Some tips:

Kill skirmishers first and kill them fast. They will randomly drop aggro, stun them when they do if you can.
The group without the skirmisher kill the Watcher first, does some nasty stuff if left alone.
Drink immediately after you kill a group, you will drop combat and those couple of ticks do wonders for mana/hp.
Make sure to pickup aggro with the tank on the casters.

The boss itself is not too bad, if you can AoE some of the adds now and then it helps.

And once you get this guy down then you get Hadronox and just when you think things can't get worse you go up against Anub'arak. This is not an easy instance, the first 2 bosses become really easy later on but Anub is a royal pain on heroic for me. AN, HoS, Occulus are the 3 heroics I am struggling with pre TOC.