Matt Williames has some "how I do it" posts. Found this part interesting:
I think sometimes it can be a downfall of animators to mistakes nice poses for "thinking" [a pose meaning thinking]. I've done it for sure-- certainly poses can evoke thinking, but i really feel like think is shown mainly in change. i.e A character is in a situation where he is being asked to make a difficult decision. He is tense, shoulders up, chest inflated, brows down-- he realized he needs to make a certain decision and is at ease with it. He relaxes his shoulders and exhales and lifts his brows. There is not a huge pose change in there, just a change of shape that shows us his thinking. You are working within a pose with something like this-- now sometimes you want to have some sort of change of line of action to make your idea clear it's just knowing where to do it
Aanimate feelings! Meaning, don't think "ok i gotta pick up the leg, move it here"--- naw naw naw, C'mon! animate feelings man! Yes, mechanics: spacing, arcs, on-model drawing contribute to good performance but they are merely a support FOR the performance. I personally feel this way, without great mechanics you can't communicate your great performance properly and yet if your animation is wonky because you don't understand good technique i think it could potentially pull someone out of the performance. Likewise a beautifully animated character from a technical stand-point only tickles the brain, not touch the heart. So while you need to be mindful to a degree at this stage of the process of technical things, your main goal is making that funny little character breath and live.