Edited part of the guide, changing it to this:
If you can pre-cast, you should start with a shadowbolt, and then haunt. Now, many people often ask why you would do this, and some people are even under the misconception that casting haunt after your DoTs is somehow more efficient. Think about it this way: Haunt should have 100% uptime for the entire fight. And since DoTs receive the bonus no matter when the debuff went up (before the DoT was cast, after the DoT was cast, makes no difference), it only matters that the debuff is up. So, why would you cast DoTs first, and have the first several ticks not get any benefit from Haunt? If you're going to have Haunt up the entire fight anyways, wouldn't it be better to have ALL ticks benefit from Haunt? Of course. The same goes for shadow embrace. The first stack is put on by that shadowbolt, and the second stack by Haunt.
So, your intial cast rotation will look like this:
Shadowbolt > Haunt > UA > Immolate > CoA > Corruption > Siphon Life. After that, you're now into what is called "filler" time. If your raid does NOT have a moonkin druid or unholy death knight, you will use CoE for your curse instead.
If you cannot pre-cast, then start with instant cast DoTs such as CoA, Siphon Life, and Corruption. Getting these up as you move into position will start your dps up sooner.