Dark Soul ability Priority (4 SSs, if less than 4 SSs remove haunt):

Use all CDs (including Dark Soul)
Apply SB:SW
Apply Haunt
Malefic Grasp
Re-apply SB:SW (as 'onproc' abilities will be up)
Re-apply haunt once you have gained an additional SS (maintain 1 soul shard through the duration of dark soul)
Re-apply Dots as neccesary
Filler with Malefic Grasp
At the last 1-2s duration of Dark Soul re-apply SB:SW for full duration Dark Soul

>60s CD on Dark Soul

Re-apply dots @ 50% Duration
Filler with Malefic Grasp
When SS > 1, and all dots "sync" (>12-16s on all dots) let them ride down to 1-2s duration then re-apply with SB:S
When SS = 4 Haunt
When SS = 3,4 and large trinket proc, racial ability, or other major CD (that is not dark soul) is up re-apply all dots with SB:SW and Haunt, then ride your buffed dots to 1-2s before reapplying.

<60s CD on Dark Soul
Re-apply dots @ 50% duration
Filler with Malefic Grasp
When SS = 4 Haunt

<20s CD on Dark Soul
Re-apply dots @ 50% duration
Filler with Malefic Grasp
When SS = 4, put up one Soul Burn buff
When SS = 4, and Soul burn buff up Haunt

Boss <20% Health
Re-apply dots with SB:SW
Keep Haunt up
Filler Drain Soul