You...have the same birthday as me. Consider me frightened
Also I was lurking conceptart and saw your post. I thought some advice/critique would be beneficial.
-Look into learning about construction and drawing first. Your people look really formless and pretty blobby. Take your time and draw simple, 3d shapes for a while (spheres, squares, etc.). Remember to draw them transparent as well, so you can figure out their.
Sure, it's boring as hell, but if you're really concentrating on understanding the forms, it'll help tremendously when you start doing people.
Good luck with improving, I'll be watching to see how you improve