1. If the lights don't move, or if there's not much moving they don't have to work as hard.
  2. Setting up 4 directional lights can make some nice AO.
  3. To get image effects to work, Set both the Min Render Target Scale and Max Render Target Scale to 1. In the camera settings.
  4. Don't use the Additive Valve shader with mesh. This will break the build by turning everything in the scene pink