I'm going to give you a critique since I am bored. Drawing, I utterly fail at so don't ask me about that. I'm also new to this guild so you should wait for someone else's critique before you drastically change your style. ^_^
First- it will be helpful to know what program you used to color these... at least for other people.
Give shading a try. The best time to suck is when you first start out you know. Any piece of art can take the next step with the effective use of dark and light. I am guessing that on
XXX white part is the shiny reflection thing. The hair needs shading too. Other than the basic "practice your anatomy" learning to shade the anatomy is also helpful. This
SSS is one of my first paintings. I made the light direction extremely obvious (well i think @.@). Try that for starters.
BAD ADVICE WARNING----{
I'd say the best thing for you to do is to bust out a coloring book. Don't worry about coloring your sketches yet. Do as many sketches as you can from photos like you did on that last one. I think you can see where you are having trouble at. When you get sick of that use your coloring book. There are many places where you can get lineart to practice on. Just make sure you don't steal or copy ^_^ Also, check out
this link!}----BAD ADVICE OVER
I don't think I really know enough to help yet, but I like to think I am useful. ^_T