I was wondering if anybody could link me to a guide for the ruffian spec. I've returned to the game after a few years off, and I'm still pretty low level (early 30s) but would like to learn how to play this class. Specifically, I'm interested in stat priorities and rotations for both single target and AoE fights.

Is this spec useful for leveling, or should I go with the other DPS spec?

Cheers.

in terms of leveling... you're better off in concealme... pubside version of concealment until level 44 as you don't have energy management in pubside version of lethality until that point.

I think the most relevant class guide is still http://dulfy.net/2017/08/07/swtor-5-3-lethality-operative-pve-guide-by-prise/

but honestly? just do every raid on SM and you'll start to catch the basic patterns, take a look at http://parsely.io/parser/leaderboard/operative/lethality/2500000/all/live/0/ for lethality and pubside version of lethality rotations to check what people are doing on the target dummies. (NOTE: dummy parses do *not* translate to raid environments. You need to adjust the parse rotation depending on cooldown usage and target availability.)