The build is simple. Heavy attack continuously while keeping up a 30 second debuff, a 20 second buff, a 16 second heal over time, and using scythe or resolving vigor when you need a bursty heal. Use your ultimate when you have a good chance for burst damage.
On certain fights, using the necromancer purge skill in place of revealing flare makes things significantly easier (for example: the iron atronauch boss fight in veteran The Cauldron where you can purge the fire debuff stacks so that you don't take increased damage and can tank the boss's channeled attack while dpsing without issue).
On other fights, it is beneficial to swap out your mundus stone, and your CP for more defensive options like The Lady stone, and ironclad instead of exploiter.