The hardest part about drawing bodies is getting the proportions right. If you use the height of the head as a unit of measurement, the average human is about seven heads tall. The bottom of the torso is generally about half way up. Women usually have longer legs and smaller torsos than men (that is, if you compare a man a woman with the same length legs the guy will probably be taller). I'm sure I don't need to tell you that longer legs look more feminine.
As with faces, the anime- or manga-style body is just an exaggeration of a regular person. The amount you want to exaggerate your figures is up to you and the style you like. Vertically, the main changes are a shorter torso and longer legs. Other than that, you just have to take the features of an idealized woman and make them even more ideal: Long and thin arms and legs (some folks like their legs very long, but it isn't necessary), small body and slim waist (yeah, yeah, and a big chest--but that isn't necessary either), usually the hips are pretty slim, and a long, thin neck. Make sure to keep the head fairly large--the human head doesn't change in size over a lifetime as dramatically as the rest of the body (I'm sure you've noticed little kids have big heads), so the smaller you make the body in proportion to the head, the more "little girl" like your character will be.
Now you have the basics of proportion to work with. When you're trying to draw a complicated pose, or elaborate clothes, it can be really helpful to find a picture in a magazine that's close to what you want, or get a friend to pose for you. That way, you can see where one arm crosses the other, or how a leg would look foreshortened from that angle, or whatever. It also makes figuring out how clothes fold or pull a lot easier. Just remember to keep them simple, too: Lots of detail on buttons or zippers is cool, but don't worry too much about getting every wrinkle and fold of fabric--a few simple lines is usually enough. For example, the image below was done based on a picture of a runner in Newsweek; any magazine can be full of dozens of great poses.