Ethereal Earring. I can't imagine playing /drk without it

. Usually I'm given double marches, so MP regen is a bit of a problem with just refresh. Ethereal helps out significantly.
As far as spells you should cast, you should have a cycle:
Stun > Bind > Sleep I > Kury > Hojo and repeat.
Note, some NMs build resistance to the above spells, so replacing them w/ Absorb/Drain/Aspir/etc is fine. Use JAs whenever they're up.
Also, keep in mind, w/ double march, you only need 15% haste in gear (since double march is 20% and WHM haste is 15%) to max recast timers. Swap in enmity/-phys%/hp as you see fit.
Hades Sainti rocks, though take care while using them. NMs like Tiamat will deck you pretty hard. One double attack w/ MS not absorbed by Utsusemi can and will kill you. I normally just swap Hades in when using JAs or when I need to do so some significant enmity building (i.e. after roar). Otherwise, Earth Staff is better (cue the -phys% is better than +enmity debate XD).