How To Reduce Noise In Cycles Render
This is a common issue with cycles, and is caused by many factors. As your scene appears to not have any glossy materials, increasing sample amount is a good place to start. If you get up near 1,000 samples, and it is not returning a good image, you can try these things:
Use Clamp This method is used mostly to remove the characteristic "fireflies" in cycles that appear when there is any quantity of glossy objects, or if there is poor lighting. Clamp indirect is especially effective.
For animations it may also be a good idea to vary the seed value with keyframes.
Multiple Importance Sampling This is fairly straightforward, you can copy the settings below.
Filter Glossy/Bounces You can use these settings to advantage as well, try filter glossy at 1 for starts. See this page for more details and an in depth explanation.
Despeckle/Bilateral Blur Nodes This method uses the compositor and reduces noise fairly effectually, sadly at the loss of quality.
Some other things to try are lamp strength and lamp size. Visit the Blender Manual for more info.