Ah, it seems all of the tutorials I used when I was starting out a few years ago have now gone. Yay for the internet? Linkdump of what's left:
Cedarseed's tutorials on DeviantART (I've linked the tutorial list cause there's plenty of other good tutorials in there too)
A lot of artists recommend Andrew Loomis' books. The story goes that they were last published around 50 years ago, which are so old that they've fallen into the public domain and are availiable to download. I haven't read them yet, but skimming over it the figure drawing one looks pretty good.
Posemaniacs: site full of computer-rendered poses you can use as a reference, to practice with and for ideas
study anatomy, study how the muscles work, study how the skeleton works, draw LOTS from real life. Draw people. Try getting into a couple of nude figure drawing classes. that will help a LOT.
if you are looking for a reference book. "Human anatomy for the artist" is a good book. The Loomis books are also indeed good. Also Burn Hogarth's "Dynamic Anatomy" as well as "Dynamic Figure drawing" will help. Just don't get too into his stuff, because his students are notorious for drawing exactly like him; you don't want that, you want to be able to put your own opinion in your art. Hogarth however is in my opinion one of the most masterful artists there is for rendering the body, the way it works, and the way it moves. The best way to make yourself better at drawing people though is to draw them a lot. You learn from your mistakes, and the more you make the same mistake, the more clear it will be what you need to do to fix it. (it takes a long time to master the figure).