Consistent playstyle. You really get a feel for your class early on. Necromancer can be played many different ways, all of which allows them to fight alone in many situations. If things go bad, they can drop aggro and teleport to safety.
The most efficient technique is to kite. Cripple an enemy, then toss up a ton of damage over time abilities and watch it wobble towards you as it dies. This allows your pet to deal damage to its back while not taking any damage.
Pet tanking: not as beefy as a mage pet. this is still a viable option.
Life-tap Tank: Not very efficient, but you really feel how powerful you really are. Drain the life of the enemy as it attacks you.
Playstyle: Caster, Damage over Time, Pet.