Cant see first pic dunno why. About the other two, they lack structure both, so what you should do is the following:
Since they have a somewhat human form (head, body and members) you can draw a human structure like this:http://www.jayespace.com/human-body/images/1776_42_100-human-structure-basic-drawing.jpg
Then redraw the character by making an outline, matching you creature.
Proceed to erase outter extralines, mantain inside lines. Draw details, like face and everything else.
Erase inner extra lines.
using a less thick pencil draw shadows, imagine the sun position, and just scribble a bit, use your finger to silde around to make good shadows.
Its hard to explain by words you must practice to know what i am talking about