It's definitely tricky, much trickier for female characters than for male ones. jwaneeta posted a little sketch once, ages ago, that really helped me figure out how to do female poses that are dynamic without being oversexed. (Still struggling with it, mind.) Let me see if I can find that post...

I loathe the sex kitten poses, so much. blch.

[eta] okay, I can't find that particular pic, but here's the link to her lj scrapbook. She's a pro comic artist and does both poses and faces masterfully, there may be something in there that helps.