In my opinion the best dk self heals are burning embers and inhale. Flame lash and obsidian shard can also be an option. Dragonblood is from my experience only worth using for tanks in pve.
DRACONIC POWER
Dragon Blood and both morphs (PvE only)
Inhale and both morphs (awesome for mobs)
Passive Burning Heart (boosts healing received when using any Draconic skill)
EARTHEN HEART
Passive Battle Roar (gives all three resources when using any ultimate)
I would recommend both Burning Embers and your choice of Inhale morph for starters. They heal and do decent damage. Burning Embers takes a bit of practice to use well.
Embers is awesome for PvE. You don't have to let the dot finish its tick, you can reapply it, and receive the healing for the damage already done. Get low on health, double tap embers, profit.
It's all about timing your rotations in a magDK, embers is going to be your most consistent and most reliable, so keeping that up and ticking on as many as you can will do wonders. Inhale is good with more targets around as it's based off how many are hit. Keep a low cost ultimate on your main dps bar for those hairy situations(dawnbreaker of smiting for me, knockdown is quite handy) when you need resources ASAP. All else fails, lock your problem down with talons or fossilize and back away to recover.