For sake of completion, the optimal start is (activate Life Tap glyph before combat starts) -> Shadow Bolt->Haunt->Corruption->Unstable Affliction->Curse of Agony and then stick to the priority list. Note that you should keep up the Glyph of Life Tap buff all the time, just consider it as another dot.
This stays true with 3.32: Even with Shadow Embrace stacking to three it is more important to get your dots upon the target than applying the last stack of SE. Reason: The dot's damage updates immediately with the third stack
, so you have to compare three dots being applied ~2s later (when you start with SB->SB->Haunt->dots) to 5% less dot damage within the first ~6s (when you start SB->Haunt->dots->SB). Applying all dots 2s later will cost you roughly at least one tick from CoA and Corruption and almost one tick from UA. For all of these spells, one tick does a lot more than 5% of their total damage, so even if SE would NOT update immediately, this would be the better choice. However keep in mind that this is highly theoretical. You won't really notice the difference in a 6-minute-fight.