Some endgame stuff can be intimidating for a fresh 50 melee. A lot of it is knowing what and when things are coming. As you practice these fights you will find yourself getting better and better as you start to know what the fight is. If per chance it is lag, there is a free trial of WTFast I'd recommend trying. It solved the lag issues on my end at least (SE is a whole other story there). Just remember if any part of you is in the aoe indicator when it disappears you are considered "in it". Also, don't "hug" a mob, stand as far away as you can without going out of range of hitting it so you have less ground to cover to get out of the circular aoe's. I'd consider myself mediocre at best so someone might have better advice but these things have helped me.