Also - don't make a habit of it, but..
If the group gets too many mobs - pick one - snare it good, get it pissed and kite it off. *Sometimes* you can keep a mob locked down that way, but don't forget to load up dots on the MT's target too.
Soon as the tank can take the mob over - you can FD
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I did that a few times with my Necro in the old days to get things under control - but be careful of when and how you do it.
Spend more time in groups too, a lot of Necros neglect to do that. That will really polish your skills.
But for now - the advice above won't steer you wrong
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And I'm assuming you know - but.. don't ever fear in dungeons.. lol