Litst is right for doing test renders. I think the two main things for fast test renders are no antialiasing and Indirect lighting quality set to preview. Here is a test render I did with no ambient light, one spot light ( not very bright ), and low to medium skylight. Indirect lighting will cause a relative increase in the amount of light in your scene depending on how many surfaces there are for it to bounce off of and fill in the shadows where raytracing did not go. Therefore, you don't need as much lighting as you are probably used to having. I would start with simple scenes with minimal lighting for learning purposes.