If the stem manufacturer sends instructions, then go along with theirs. If they don't, then as a best practice, you might want to put it together and begin snugging the bolts gently by hand while making sure the faceplate is going on evenly (assuming it's designed to, unlike my Salsa SUL-type stem). Once you got to where it was getting a bit of clamping pressure and was obviously coming together evenly, then you could bust out the torque wrench, set it for 1/4 of the final torque spec, and begin giving the bolts 1/4 turn at a time, in some sort of rotation pattern, until you began getting the desired torque on all the bolts through a couple of rotations. Then raise the torque on the wrench and go through it all again at the new torque setting.

Where I'd bother with that, is delicate or sensitive parts (carbon steer tubes, carbon bars, carbon frames, ultralight stuff). If I'm slapping my old mountain bike back together after an overhaul, it being all old-school durable stuff, I'd never bother molesting my torque wrenches just for that.