Presentation.
your presentation of your models is also really harming you. A good model badly presented can look bad and a bad model nicely presented can look good.
the first thing I suggest is for you to make a flat plane so you have something to to catch shadows and then place your model on that. thens set up your lighting.
with lighting remember you need the following
A Key light (basically the light that shines on your model)
a fill light (a light that casts no shadows on yout model, but keeps the scene from being too dark)
and a back light.(this light keeps the shadows on the back side of the model from blending in too much with a dark background.)
this should help your presentation a lot, it will also help others see your model fully and be able to critique for you properly.
here is a site to help out with lots of different programs, including all the primary 3D programs. give it a look and do a tutorial or two, it will help.
www.tutorialized.com