The point of a pre-viz is to test-drive the spatial mechanics of your story - to ensure the camera work is precise, emotional, purposeful - that the story reads etc. In terms of polishing etc., seek to create atmosphere through lighting where and when appropriate, but this isn't a 'digital set' project as per last term - the holy grail lies in ensuring your pre-viz supports/enhances/enriches your animatic by delivering the complexities of camera and actual movement in a way your animatic cannot.