First off make sure the piano is tuned. I akin recording an out of tune piano to a litter of kittens dying. But I digress... Secondly, it depends if you're recording at home or in a studio. If you have access to more expensive mics, then go for something like the AKG 414s, Neumann U87s or KM84's, or my personal favorite.. the B&K 4011s. If you don't have access to something of that sort, a pair of Shure SM57s should suffice....they're cheap and they'll get the job done although they won't capture as much detail as a condensor microphone. If you're going for a more pop rock kind of sound, use a space pair pattern near the hammers, about 3 inches off. A space pair is when the two mics are placed parallel to one another with a space between them. Try starting off with about 9" in between the two, you can play around with this till you find the sound that's most pleasing to you. If you're aiming for a darker sound, place one mic over the high strings, and one over the mid to lower part of the strings. Experiment with exact placement until you find the sound that you want. There are other different mic placements to consider, but a space pair should get you well on your way. Good luck!