Graininess is usually a result of your lighting. If I were getting a lot of grain, I would start by turning up my main light a bit, or if you have one light that is pointing at where you are getting the grain, turn that one up. Start by turning up the intensity of one of the lights and experiment.

Blackhearted posted in a thread on here that he plays with his lights all the time to get a better render. I used his here for this image, but also played with a couple to get them where I wanted.