Step 1: Skeleton
Sketch your basic structure outline. For the torso we will of course need the vertebrae, ribcage and pelvis. Don't worry about sketching these the -exact- shape of the actual bones. Note that on average, the female shoulders and ribcage are more narrow than the male's, and the female hips are wider than the male's.

Step 2: Muscles
Sketch in the general shapes of the different sets of muscles. Check your muscle layout with an anatomy chart or constructive anatomy book. Number 1 marks the top of the iliac crest, where the pelvis protrudes a bit. Number two marks where the meat of the leg bends. Here is a very important item: breasts come in a variety of sizes and shapes, and they are chiefly comprised of fatty tissue. Breasts will look different depending on whether the figure is clothed or nude. Breasts react to compression, and they are effected by gravity.

Step 3: Skin
In this stage, you're making your sketch look like it is a normal, naked torso. Decide which areas should be defined, darkened, or lightened. Good references for this stage would be a fitness magazine, sketches from a life drawing class, or a constructive anatomy book. A horizontal line through Number 3 will show the placement of the nipples. Important items to remember are that the average female body has more body fat than the male's (yes, this is both normal and healthy), and the average male's body has more muscle mass than the female's -- especially in the upper body. As such, you will notice less muscle definition in the average female, lending to a smoother and more curvy figure versus the more angular male body. Sometimes, it appears that the rectus abdominus muscles on a female flare out at the bottom all the way to the iliac crest; however, this is not the case. The swell of the lower abdomen most often masks the delineations of the underlying musculature depending on the lighting on the figure and the figure's stance.