D/Mo Build

Can anyone suggest a good PvE D/Mo build for somebody with no proper experience with Nightfall or Dervishes specifically, but some experience with Guild Wars as a series?

List your Dervish elites if you have any, this will enable us to help you.

As I said, I have no experience with Dervishes and by extension no elites or skills aside from the ones you get from the first few quests--I'm open to suggestions, though.

With low energy from avatars, only Balthazar/Dwayna/Lyssa are options. From these 3 I'd suggest Dwayna - cheap, healing and hex removal.
If you want to breeze through mobs, Wounding Strike is a nice elite to have - unconditional DW, yummy.

You bar basically should look similar to this pattern:
3 attack skills ; 3 defense enchantments ; 1 offense enchantment (IAS etc.) and a rez.

Nice attacks skills: Victorious Sweep, Mystic Sweep/Eremite's Attack, Zealous Sweep.
Nice defense skills: Mystic Regeneration, Mystic Vigor, Faithful Intervention, Vital Boon.
Nice offense skills: Pious Fury (even with short duration synergises well with Vital Boon for healing), Heart of Fury.

Hope that helps at least a bit.

Balthazar is terribad. The buffs don't synergize at all except for running, and even running there are better skills. Don't use it.
Dwayna and Lyssa are pretty good. Lyssa and Aura of Holy Might allows for some pretty ridiculous damage numbers. Dwayna is good in hex-heavy areas, and Mending Touch compliments it nicely.
Wounding Strike is nice, you can pretty much just tab through targets and apply DW where needed. Reaper's Sweep, similarly, is decent, with the largest +dmg of any scythe attack.

Personally I'd stick to good ol' Melandru. You'll need a +20e staff or +30/-2 set to afford it though. 14scythe/13myst; Wearying Strike, Victorious Strike, Zealous Sweep/Wild Blow, (Zealous Renewal if you didn't bring Zealous Sweep,) Heart of Fury/Pious Fury, Eternal Aura, rezsig/sunspearsig, optional.
You can bring Mystic Regen on a Melandru build too, but I prefer the mysticism.