Utilize several microphones for a better range of tones. If your amplifier does not have multiple input jacks, you'll need to get a few XLR cable splitters to plug several microphones into the same input jack. For each microphone, use a different boom mic stand for easy, individualized adjustment.
Use stereo sound unless you are seeking a rigidly classical sound. Designating one group of microphones as the left and the other as the right provides a more interesting stereophonic output. However, some musicians still prefer mono output for a more authentic experience.
Position microphones above the strings, just underneath the piano's lid for live, stage-based amplification. Place all available microphones at equidistant intervals across the length of the piano. Positioning microphones close to the piano's inner components will provide the loudest projection possible, ideal for packed recital halls when volume is important; however, to mic a piano for crisper, cleaner recording-based recitals, a different method is preferred.
Position microphones in the center of an acoustically resonant room. Square rooms with hard, wooden surfaces work the best. Ensure that all doors and windows are closed and all furniture has been removed from the room. By allowing the sound to naturally echo through a resonant space prior to being captured via microphone, you'll have ensured clearer sound quality. This type of microphone usage is only conducive to personal recording, and obviously cannot be duplicated on stage.