How to decrease render time for test-renderings:
a) The main setting to decrease the render time is the image size.... you can use a small resolution, it may be too small to see the object's details but it’s perfect to understand the light conditions.
b) Lower the Shadow quality
c) Reduce the polygon number of the objects (try to use the optimize modifier if you don't have any mesh smooth modifier on the objects)
d) Reduce the photon number or/and the "sample" settings in the render engines. Vray/MentalRay/Brazil RS/FinalRender/ etc
e) Be careful with the amount of lights (too many lights will make the rendering very slow)
