Really the best way to get better is to just keep looking and keep drawing. There are a lot of books out there, too. Looking at artists you admire helps.
The only real suggestion I have about that drawing for the hair is to not focus so much on making hair purely out of lines. Get about 3 tones, light, medium, and dark, and use them to block out the different shades of the hair. Then with the light and dark, add only a few lines to make it seem more like hair. It will help it look more realistic and less medusa.