Might I suggest studying photographs of real people that have been shot with figure study in mind?
artists.pixelovely.com/practice-tools/figure-drawing/ and
www.quickposes.com/pages/timed are both practice tools based on this idea. Doing actual real-life studies of a model posing in front of you is supposedly the best, but it's not very practical if you're not an art student (social sciences person here, I've never done it) so well-shot photos can be a good substitute.
Anime anatomy is, of course, based on real life, just exaggerated, so understanding how real-life figures work is a strong basis for drawing anime characters in any style. I think you'll notice that the most talented anime artists have an extremely strong grasp of human anatomy. The biggest difference between anime characters and real people is the face, and even that is still just a caricature of (usually East Asian) human features.
As for how to go about studying figures, I think understanding contour and gesture drawing is a good place to start. When it comes to constructing figures from scratch, the mechanics of perspective and proportion are essential. My favorite books on drawing that I've found so far are anything by Loomis (although they can get pretty complicated, too much so for me!) and Kimon Nicolaides's
The Natural Way to Draw, which is extremely hardcore but awesome.
I think that overall, there's no substitute for studying pre-existing figures. Since your goal, I'd assume, is like mine--being able to draw figures from imagination--you do need to practice that, but I think the majority of your practice should be figure and portrait study. It's really less frustrating than drawing from imagination because you have something to compare your drawing against instead of just guessing.
And do note that since anime proportions and realistic proportions do differ, there will be some adjustments between the styles, but IMHO it's easier to start with realism and work off of that.