This is what I do at work all day....
Learn the anatomuuuus! I brought my trusty anatomy book to learn all those bones and muscles >.> Stringy arms are still giving me grief though..specially the lower portion of the arm... those muscles are so complicated? whyyyyyyyyy????!!!!
So what have I learnt? I usually have trouble with the part where the clavicle makes an indent on the skin on the shoulder. But since I know where the bone is now it will be easier to get it in the right place
Refer to the top left corner.
Tip of the day? get an anatomy book OTL they really are helpful.