a good proportion i used with classical drawing was about 5 and a half heads for overall height for a "youth".
 
so from the middle of the coller-bone (clavicle) to base of crotch (pelvis) will measure 2 and a half heads, then from the base of the pelvis to the base of the feet (tarsus) will also measure 2 and a half heads, if you then find the middle position between the knees (patella) and the top of the head (cranium), that will give you the ideal place for the belly button (umbilical)

also the length of the forearm (ulna) from elbow to wrist is roughly the same length as the lenth of the overall foot.

The "notesbooks of Leonardo Da Vinci" will give you more info on scaling the Human figure.