@newsmuffin/any anatomy drawing hopefuls: a few anatomical tips.
1) 'normal' (see: idealistic normal, not real life normal) people are 8 'heads' high, as in their head is 1/8 of their total height. however if you want a 'giant' character 9 is better, and you can use 6 or 7 to make short characters.
2) the wrist of an arm should reach roughly to the horizontal line crossing the center of the pelvis, can be measured by getting the rough distance of the two sections of the arm, accounting for any changes made by the rotation/perspective of it, and seeing if it is roughly the same. (no need for a calculator, accuracy within 20% will still look normal enough)
3) other then those two just keep in mind every little 'neat fact' you have heard about human anatomy (all those ones 5th-8th graders find so fascinating)
(you seem to have gotten it pretty good, just the arms in the first image looks a tiny bit odd, and the head is a little small for 'realism' in each of them. however as always, fuck realism, artistic liberties come first and foremost.)
EDIT:
@Newsmuffin: your idea was neat enough and easy enough that I decided to steal it for practice on my tablet.

even added a credit box so people finding it via other sources know its not my idea, hope you don't mind too much.