start with beans and tubes building the mannequin off your gesture. remember the draw over, under and around the forms.
It can help to define the space the drawing fits in using marks on the page to indicate "live drawing area"
Once gesture is in, start builsing up tube forms...break forms into sectioned tubes to figure out foreshortening
build up contour lines into more final lines, using line weight to indicate shadows, where objects meet, fall into darkness and move into foreground
use a single tone to indicate value. try to restrict values to 3, black,white and midtone grey. Think of shadows as shapes that connect forms of the body.