GI/AmbOcc/FG workflow

• Create a light in your scene and enable photon emmission
• Disable use default lighting in the render settings
• Use the default quality settings and render
• optional: attache a MR physical light shader to the light. This approximates physical lighting through the value of the light's color. A way to derive an accurate value setting is to divide the photon intensity of the light by PI (3.14). 
• optional: attache a mia_exposure_simple node (under Mental Ray lense shaders) to the camera(s) you are using to render. This will enable fine-tuned exposure control for your lighting.
• Increase Photon Intensity until you can see the image or have the brightness near what you want.
• If the Photons hits are splotchy (and they will be) increase the number of GI Photons emitted.
• Raise the Accuracy by 200 until you can't see much difference. Go back to the lower setting when you couldn't see a change.
• Is there enough detail, or is it looking soft and blurry? If too soft, increase the number of photons.
• Use the map visualizer to see how the photons are hitting in the scene. Adjust your light source? Add in additional lights?
• Adjust gain and compression in the mia_exposure node 
• Use MIA_material and enable ambient occlusion. 
• You might now need to decrease your Photon Intensity (because you now have more photons illuminating the scene).
• Again, raise accuracy by 200 until you can't see much difference.
• Repeat until satisfied.
• If you decide to add in Final Gather to help smooth out results:
  • Turn on Precompute Photon Lookup in RenderSettings>IndirectLighting>Final Gathering Map.
  • Try immediately decreasing by 1/2the number of Photons emitted . You probably can get by with less and this will save you render time.
  • You may want to increase the Photon Intensity so its effect is still evident.
  • All the normal Final Gather attributes come into play now and need to be tweaked.
  • With Global Illumination turned on, Final Gather will not use "Secondary Diffuse Bounces" Keep that at zero.