Loganisis's has a very good primer:
If you read a little bit more on these forums you will find a lot of discussion of the rotation. Typically, the focus is on the single target rotation, which I gather is SS-Dev-Dev-X where X can be some filler and where Dev can be replaced by Revenge if it procs (that can be good if 5 mans if you have specc'd so revenge hits a second target). You reset if you get the proc that allows you to use SS again. I find the heart of 5 man tanking to be "cleave tanking": you mark one target with a skull as your party's main target, then you apply "splash" damage to a few other secondary targets. For the secondary targets, you probably want to be applying rend, spreading it by thunderclap via the Blood and Thunder talent, using cleave when you have rage (50+?) and shockwave on cool down. (You can tab target if need be.) Balancing out your threat on the skull and your threat on secondary targets is something of an art, and I can see how a mage AOEing stuff can cause problems while levelling.
In wotlk, people tended to AOE a lot but Cata has made that often less efficient - so there is no shame in telling the mage to focus fire on skull and avoid AOE. Or just let them die do they learn the hard way. Asking them to sheep a caster can also make your life a lot easier in some fights. You'll find CC very useful when you don't overgear fights; it also reduces threat problems.
The add-on Tidy plates and Threat plates are very useful in helping with aggro problems with trash - they make it much easier to see when you are losing or have lost threat. A threat meter like Omen is good for boss fights.