There's not really much of a guide, except to properly spec in the Shadow tree. I'd be looking at something similar to this as a goal levelling up:
http://www.wowhead.com/?talent=rxMhkhhZbZgMGtMzRhtxo

It's kinda of a clusterfuck build, but it's mainly geared toward PvE grinding, so it skips all the crap that debuffs giving increased damage as they're never on long enough to make a difference while grinding. I basically would focus on doing more damage efficiently (less mana spent and regen) with added +shadow damage than worrying about wasting time spamming up a mob with Rank 1 Pains to get bigger numbers on your screen, heh.

Other than that, just quest normally.