Get a pair of good microphones. Using two microphones is the easiest way to record a grand piano. If you don't have two microphones, borrow one or pick one up through an online discount music gear supplier.
Set up your recording equipment. If you are working alone, set the recording gear up within easy reach. Make sure both microphones are recording and working properly before you position them on the piano.
Position the first microphone. Open the top of the piano and place one microphone about 10 inches above the strings near second G, below middle C. Make sure the microphone is facing inward.
Position the second microphone. Place the second microphone the same distance above the strings, this time near second G, above middle C. Make sure the microphone is facing inward.
Start your recording. Do a brief test recording, then play it back to check the mix. Adjust the position of your microphones and settings if necessary. Repeat until you get the perfect sound.