You got some nice concepts there, but you seem to be concentrating too much on being a digital artist.
Try to become even greater with a normal, analog pencil. Do gestures, expressions, difficult geometry.
Then go back to your computer and see how much better you've become.
I definetely see some potential here.
I'm glad that you've decided to start a sketchbook. Use it as some incentive to keep drawing; the only way to get better is to practice!
You're at a stage now, where you need to train your eye. Keep drawing from life, and if life is not around, try some pictures.
If you want to be able to draw from your imagination it would also be a good idea to mix in some drawings from your imagination. But make sure to keep in mind the things you drew and learned from the life drawings.
Thanks for your comments on my apsaras drawing in the WIP and Critique sections. They're definitely helpful.
To follow on the "training the eye" thing, I suggest looking at the book "Understanding Comics" by Scott McCloud, whether you plan to draw comics or not. Libraries often have it. There's a section in there on realistic vs. iconic drawing. The iconic version of an eye (the one we all see in our head unless we pay attention) is your basic football shape. But that's not how they really look. To train the eye, we have to set aside our preconception and draw what's there. A useful exercise for this is to draw a picture of someone from a reference photo that's upside-down. (Got that from the book Drawing on the Right Side of the Brain.)
Also, here's a tip for scanning. Put a piece of blank paper behind the page you want to scan in a notebook. It keeps the image from the page behind from bleeding into your scan.