well, if you are looking to stylize, it may just make sense to go with a particular disproportion if it can be done consistently(in which case you'd just keep practicing it until you fall into a good groove), or imitate a bunch of cartoonists you like until you get to the point you want to be at. but if you wanna do stuff that is well- proportioned, and looks realistic, you really need to base your figural studies off of the, well, figure. draw your hands, draw your feet, get someone to model for you, and draw their whole body over and over again. it also helps, in both cases, to find good references(anatomy books, etc.).