Primary : Poison darts + Splinter
Secondary : Anything you want, i like haunt + consume for health back
Defense : Spirit walk + Jaunt
Terror : SOUL HARVEST + Siphon, Languish or Soul to wast
Decay : Acid cloud + Acid rain or corpse bomb
Voodoo :Big bad Voodoo + Slam dance
Passive 1: Gruesome feast
Passive 2: Pierce the veil
Passive 3: Spirit Vessel or Grave Injustice
You're going to get poison darts + splinter because that's the highest single dps skill for the witch doctor. The atk speed goes directly into play for that skill.
What you're going to want to do is to use Spirit walk + jaunt for the extra time and soul harvest everything you can for max stacks.
Take some distance and use 1 Acid cloud, this should do huge amounts of damage to the enemies.
If there's some red orbs, take them to activate Passive 1, this combos well with passive 2 since the damage stacks. Passive 3 will keep your health high or at least keep you from dying.
Use Voodoo if there's enough enemies to warrant it.
The best part: This should make you shoot darts incredibly fast and you should be doing massive amounts of damage. VERY GOOD AGAINST BOSSES.