Don't beat yourself up too bad. I still have pulls that I lose 1 or 2 toons or sometimes wipe. If this is consistently happening maybe pop bloodlust and trinkets on these pulls. Switching targets quickly is a big thing also. I found that if you take too long on switching targets things get out of control easily.

Be sparring with chain lightning. I only use chain lighting if I can kill the first mob instantly. If this is the case I shoot a lightning bolt then cast chain lightning. Both of them seem to land at the same time. Then I switch over to the second target and take them down with lightning bolts. If you have multiple mellee mobs in on you don't use chain lightning as this will pull them off of stoneclaw.

One thing that I wish I learned to do was earthbind kite targets. Search around for Xbox videos. In his heroic SP he shows some pretty nice earthbind kitting.