If you have never taken a life or gesture drawing class, you really should. It will take you much further than any anatomy book can. here are some resources to get back into the swing of figure drawing
You should block in the fugure by trying to quickly capture just the general, large shapes of it first. try to do at least a few drawings looking at the figure only and not at your paper. If you haven’t read it, “Drawing on the right side of the brain” is an excellent resource to start out with. Burne Hogarth’s dynamic figure drawing books can take you a tiny bit further, and Loomis has several big books on blocking in the figure and its anatomy that will take you even further along.
Try to keep your drawing loose and without detail. If you set the limit to 30 seconds this will get you going in the right direction. Waste some paper. Don’t think of these as finished drawings or even as something you can later use as a finished piece. Loosen up your wrist and elbow, draw as big as you can. Plan to throw away all but one of a dozen sketches from the figures. This gives your hand and mind a little more freedom.
It’s practice. Practice makes perfect. It takes some time to get a natural feeling for the human figure, but doing a half hour to an hour of really loose sketchy figure drawing two or three times a week will get you very far very fast.