ok here is what i do for my mental ray renders.

1. apply shader to model, floor, and dome. (i prefer blinn for the model and lambert for the dome, and blinn for the floor).

2. then for the shader of the model and floor, choose ur color, then increase the ambient color a little bit. then decrease the eccentricity some. increase the specular rolloff and mayb increase the reflectivity.

3 then for the dome shader make the color a little bit less than full white. increase the ambient color some.

4. make a light and set the intensity to 0.

5 in the render globals change to mental ray. then under the mental ray tab change the quality to preview final gather. then go to the final gather and change it to 350.

6. then render