Just an advice that I got a while back, so I thought I pass on, could help you too;
A good way to improve is to study other's drawings and drawing from life. So here are some tips:
- Every day, draw 1 page of posemaniacs: http://www.posemaniacs.com/?pagename=thirtysecond
Start at 90 secs, then work your way down over time.
- Study from Loomis, Bridgeman and Vilppu's books.Visit my sketchbook's very first post
for some useful links and books.
Copy their drawing and try to apply what you learn to your imaginative stuff.
- Draw stuff from life. Everything goes pretty much. People on the train, bus etc. Your dishes, shoes, cellphone, your hands, everything.
- Copy drawings you like. Just remember to say who your copying. and try to understand why the original artist placed the lines where he did.
- If your can find life drawing classes with models near where you live, go to those. Drawing from life is pure gold.
Drawing from imagination takes ALOT of work. Before you can do it properly, you need to study and create a library of shapes in your head. The aforementioned tips will help you build this library.
I see that you are a hard worker, so if you don't give up, then there is nothing that can stop you from improving and from becoming a proud quality artist.
Keep drawing and post your newest stuff!