Creating textures and materials is a key component for great looking CGI images. Lighting and composistion are crucial too, however, without the right 'finish' a product can look flat and unrealistic.
I gave myself a challenge of making a set of low poly toy soldiers look awesome using only simple lighting and framing. I put a tremendous amount of effort in to producing great textures and materials, focusing on isolating the soldier from the studio background and highlighting the gun. I love the results, what do you think?
The beauty with CGI is, if you can imagine it, chances are you can produce it!