My advice is to use stock such as jupiterimages or thinkstockphotos. Amazing quality. For fashion, if you ever want to peruse around;
iPartment -- it's a Chinese website.
Also, I don't know what you're going for. I know I lean more towards stylized realism, but some people are major fans for the kawaii over the top stylized sketches with the large eyes.
For realism, here are some basic rules (you can actually try many of them on yourself and see that they'll work);
Foot = forearm
One eye = distance between both eyes and eyebrows (eyebrows can be an exception if character/subject plucks/waxes/otherwise takes care of eyebrows) AND equals nose
Length of hand = length of face from chin to hairline (I'm an exception due to my own small lil' fingers)
Lower body = torso + head
Calves = thighs
For men their heads are straight while the women tend to decrease as in / for circular bit of head to jaw.
Ball of shoulder = width of bicep/arm in general AND the thickest bit of the forearm
Women with their ratio of shoulders to hips; ones who have never exercised (weight lifting) typically have / smaller shoulders wider hips, those are are moderate/born with broader shoulders | | while those who over did it a bit (it took me a 155 lb of squats, but I managed to do it) / so it appears they have narrow hips, but typically the case is that they have broad shoulders (something you'll definitely notice with models).
Men have their hips start lower, women higher.
Men's fingers typically remain equal in thickness while women's are prone to thinning out towards the tips /.
Then again, it's really about style. Although, I've always believed to be able to bend the rules -- you have to first learn them (otherwise, there will seem to be things that are "off"). Besides that, it's all about intuition. When the light goes off and it hits ya, "Ohh!"