Gentar :D \\o/
dying_inside, definitely resize these babies! ;) Images exceeding 3000 pixels in any dimension are only good if you are trying to show off an insane level of detail. For sketches, keep them below 1000 pixels in width or height. I would recommend below 800, even. A really large image size requires the viewer to scroll all around and try to piece the pieces together instead of being immediately presented with the entire drawing. You can also cut off the bits your scanner catches that fall outside the image, or your sketchbook - the GIMP is a good free program, similar in many ways to Photoshop, that will allow you to do these simple manipulations that really enhance your presentation. This is most important right now.
There are some really cool concepts floating around in your images, but I think they have to be polished more - anatomy, as Gentar mentioned, and I think right now just clean smooth lines. Just because something is a sketch doesn\'t mean that it has to look sketchy ;) Once you have established your basic subject, erase extra lines and clean up the paper.
Consider giving your figures not just shape, but bulk. Not everything is composed of purely straight lines, or pure curves. Sometimes shapes blend and merge into each other, to create a sense of fullness. This will be more apparent once you poke at anatomy some.
I would suggest that right now you leave shading out entirely and just concentrate on line and shape. Once you understand how figures are composed, what geometric shapes they are made up of, you can concentrate on giving them visible volume through tone.
