I'd say it might be best to look up a couple of tutorials on the subject. I wouldn't advise diving in and trying to model a character straight away. It's the kind of thing that you won't quite be able to get to feel quite right, from my own experience. But when you do get around to it, the best thing for it would be to get an orthographic of what, or who you want to model, rather than freehanding it. At the very least it'll help get the proportions right!