Just thought I'd add my two cents in.

Everyone has already given you great advice, I'm currently levelling 3 Shamans at the moment and I have two elemental and one enhance (my main), when I'm about to attack something, I use a macro to make the casters stop a little bit behind my main so that I can go and get the mob and keep it infront of the casters. Even if they take aggro (which happens all the time) the mob runs to the front of them and they can continue casting, also in pvp it means that not all 3 can be feared as they are too far away.

3x Tremor totem is a god-send also, if they do managed to get feared, it'll only be for a second maybe, maybe not even so, you can quickly hit your follow key and stop key to make them face the same direction and continue on with the onslaught.

Of course I'm still working it out myself, with being only level 47 at the moment, but in all the PVP I've come across this has been the best tactic by far.