I'm currently level 35 lock, these are the skills that I've put points into and I can kill monsters steadily without the need to rest very often. I went from 30-35 pretty quickly, I was at 30 only a couple days ago.
These are my skills at 35 currently:
Fireball (4), Lightning(4), Meteor(3), Ivy(3), Will domain(3), Vampirism(3), Soul Keeper (3), Mana Borrow (3), Ambitious Sacrifice (3), Dragon Blood (3), Mana Pool (3), Arcane Devotion (3), and Energy Barrier (3).
This allows me to be dealing damage, minimizing damage taken with control spells (ivy,wd) and energy barrier, and balancing hp/mana with mana (as, mb) and necro spells (vamp,ss) to keep going without often needing to rest. Arcane Devotion (icreases cast speed) also allows me to kill things before they even get close enough to hit me quite often.
Hope that helps. G'luck