I like the bag :3 Want a few suggestions?
Whenever you're coloring or shading, don't be afraid to push the contrast higher and higher - to make the darks really dark and the lights really light. Not so much that the detail disappears, but strong highlights and deep shadows bring a lot of volume to an object. There may be that scary thought of "Ican'tIcan'tI'llruinthepicture" when you test things out, but learning has to include experimentation too :]
Scale your pictures down. I've noticed that you have some at the colossal size approaching 1200x1600 pixels. For sketches, unless you are trying to show something really intricate, try to keep within 800 pixels in either dimension. And if you have a lot of objects to show on one page, you can help yourself out further and just draw the objects closer together. Try to trim off any excess white space off an image as well.
Have to run off for now but I'll be sure to come back and comment some more! You have a good gallery :]
