Instead of using dof in physical cam, Photoshop can do the trick with zbuffer channel or plugins like Alien Skin’s DoF and DoF Generator PRO by Richard Rosenman.Be wary of glossy reflection and frosted materials.(case to case basis).It's up to you if you want to drink and eat and sleep until the rendering finish. Be wary of iteration levels when making curves/mesh smoothing.I always shutoff my antivirus while rendering (or don’t install one at all).Get rid of the undo window, especially commands on the list that eat up memory….Know the difference between copy and instance… Simple but effective.Use high polygon objects only when they are close to your camera.Try to use your own materials rather than prepared. A simple diffusion, bump and reflection(with.

Material wise: avoid using too much glossiness and highlights.If you render your final image at 3500px you don't need more than 4000px image anywhere. Remove unwanted objects from your scene.Don’t put too many subdivisions on your shadows (as much as possible).If you are using Vray, always proxy the ones with high polycount.The more polycount, the slower the rendering. Limit your polycount to minimum as much as possible.

V ray render