Also don't forget that Flash has a very small radius. Watch for the "Blind" effect text that will show up next to each enemy. If it doesn't show up, it means they were outside Flash radius.

Also you must upgrade your weapons! A general rule of thumb is that if you are using anything that is 5 levels lower than your character level, then you should not expect to adequately maintain enough enmity in a dungeon. For example using the Lv.10 weapon in Sastasha, you're almost guaranteed to not be able to hold aggro.