depends on what version of maya you have.

i believe 7.0 and later have the 'ambient occlusion' preset found in the render layers tab (which shares its space with the display layers).

click around in there and you'll find presets. switch to ambient occlusion and if i remember correctly, it turns everything in your scene green. render. (it should also automatically switch you over to rendering with mental ray.)

another way is to open your camera attribute editor, and in the environment tab (scroll down a bit), change your background color to something other than black (mid-gray works best, but adding color doesn't hurt). then, change your rendering to mental ray in the render globals (render settings, whatever). go into the final gather tab and turn on final gather. the default settings for final gather should be fine. change your mental ray quality settings to production, and render.

each of those methods should take you less than 30 seconds to set up.