I don't have one of those graphics tablets I had to learn to use the mouse to draw with in gimp, it definitely takes a lot of practice! Don't give up though your skill will develop just like it did when you first picked up a pencil, same thing. If you would like advice on a regular basis check out my blog at www.wix.com/lejprints/ljames I have been drawing since I was a little kid and i still have much to learn but I am willing to teach what I know.
It seems to me like you have the right attitude and drive... those two alone are the biggest assets you can have. Just keep at it.you're doing a great job! Now its all about exploration. Learning new things. Little by little. Good luck and keep rockin!
If art didn't teach you perspectives, then you would have to draw from a reference you learn from life, and life will never guide you wrong with perspectives.
It is the constant things you notice the most that guides you, but if that is only your art then the world you create needs more real life.
I know for a fact if you look at life for things you see everyday, something in the back of your mind will say you see that all the time, so why look. The truth is you see it but you never studied it. If you draw your hand your mind will tell you if you get it right or wrong, but it will not tell you how to draw it. That is something you need to study and know as an artist point of view. In that point of view, you not only know what it looks like, but you understand it's structure.
Having a 3D sturcture of every joint and the structure of each section means more to the artist side than just draw and I will tell you if it is right. There are thousands of ways to do it wrong but only one way to do it right, and that is what you need to tell yourself just to study every detail you need as an artist knowing you have seen it more times than you wanted.
I see your art has what you learned, but little from knowing real life. Perspectives is not something life can be without.
Well what I would recommend first of all is to work on your lines. They look really stiff and that your characters/subject matter swallowed a ruler ^^ *no offense* Make your lines flow a bit more smoothly. Also, what I notice about your shading is that it's very flat and that it looks like you use greyscale to shade. Adding a bit of violet or blue may help your images pop a bit more. Try to add some contrast and your lighting is a bit weak. Use lighting and shading to define shapes. I would look into color theory. You look like you're getting a grasp on anatomy but so far, there's no defined style, it just seems like you have numerous style. To start off, try to find your style that defines you. Then do some research on lighting and color theory. :3 Hope that helps ^.^