[guineapig]

I used to always spot-heal and twitch in groups with my necro on live.

Use lifetaps as your nuke since your loosing hitpoints anyway due to your mana regen.
Position your pet well so it can do maximum damage from the back of the mob.

Lower level snare (forget the name) is great for mobs that run and a nice additional treat you can give to your group.

Crowd control. You have a short duration mez, usually plenty for single adds. Use it!

In extreme case you can be a puller to split a camp for the group. Rarely necessary with so many forms of lull, and other classes that can FD, but it's still an option.

Buffs! You have resist buffs! If your mana is good, use them on the main tank and/or puller. You would be surprised how often the tank and puller have dots and/or debuffs of some kind. This lowers group DPS and increases the mana that the main healer needs to spend.

Necros have decent versatility when you think about it. Much more so than a mage or wizard.