Firstly, I would set the camera to the highest quality setting it has to capture as much detail as possible with minimal jpeg compression. As for grain / noise, you are at the mercy of the sensor. I doubt you'll be able to choose the ISO of the camera so try and take photo's in bright conditions which should set a low ISO, eg 100 or 200 and keep grain / noise to a minimum. After that, Neat Image used appropriately (minimally!) as OPSO1 suggests can be helpful.
Equipment: 2x Canon EOS 50D; Sigma 10-20 EX DC HSM, 50-500 EX APO DG, Canon 24-105 f/4 L, Speedlite 430EX