You're off to a good start, by actually taking time to do models and not quitting after your first attempt. You use a lot of pre-designed shapes, however, and that is not a good way to do things. Like pappenheimer said, use those tools to be your main design tools.
Also, I would suggest investing in a better modeling program, or if you do not want to invest money, there are quite a few free ones out there (wings3d and blender being my favorite) And for skinning, there is the GIMP, a great 2d tool.
I would suggest looking through
This Thread to find countless other tools and tutorials that will help you become skilled with game designing.
