If your going to get upset at me about this please search my username and look at my previous post (ages ago) about melee's helping out the casters.
A hell of a lot of DDO casters, especially nukers, especially at mid-level, have no sense of strategy in some respects. The following is elementary in any mmo I've ever played.
1. Kite towards the melees! They are swinging their hearts out, run straight through them, put the mob within striking range, and there's a good chance they'll just take the agro. Once they get it, don't throw a spell and take agro again and run away.
2. Don't spread aggro This is a chronic problem when people get fireball and firewall (hey and what about acid blast? I'd love to see some more acid blasts). When me and my sword swinging buddies charge in and you throw a fireball / firewall / aoe spell at them from behind, they charge [/u]you[u]. They run straight past us, so we can (a) turn around and chase them or (b) keep moving and hit their casters, keeping in mind that their melees are now chopping on you. And neither is a good option, because whatever you we do, you are going to run away and we are going to end up chasing them.
Seriously, on nearly every quest I end up running after an AI melee who is running after a caster.
3. Shoot at ME! If you wait, me and the other sword swingers will charge in and hit the melees who will barely have time to move before we're wailing on them. We take two steps and we're into their casters WITH their melees grouped up. Time for Fireball/Firewall/AOE. NUKE EM. If it's a trash mob, wait. If we aren't taking any damage, don't throw it. Wait til we need you and make it a NUKE. Maximise it, Empower it, get gear whatever you need to do it. Whatever you throw should clear the room, and it will, if you wait.