I strongly recommend that you place the microphones as close to where the hammers hit the strings as possible. Pan anywhere from nine and three o'clock to hard left and right for stereo, you should always check in mono for phase cancellation. Cardiod microphones work best. They cut down on leakage and pickup less from behind . Using EQ and compression will add noise to your recording, so be conservative in how much you use.
Compression can reduce the dynamic range of the piano and result in a low quality recording.
This holds true especially for rock, jazz, classical and on ballads. When you're trying to record rock piano in a room or on stage with loud amps, you're not going to be able to use those omni-directional patterns. To minimize feedback, cover the piano with blankets or a custom shell. When a more mellow piano sound is wanted try and mike the piano from the rear as well as the right side, keeping away from the hammers hitting the strings and focusing more on the soundboard. If you don't have expensive tube microphones to work with, try the dynamics.