The piano is also one of the most difficult instruments to get a great sound from. There are so many harmonics and playing styles to work around. You need to know the genre of music/style that the piano will be doing. Also, how the player plays it. Light? Aggressive? Dynamic? Rock? Country? Classical? Jazz? Yikes!!!!! 😛
Solo piano will require a pair of condensers aimed at the side of the piano where the lid opens up. And most likely the lid will be fully open for this type of playing. Mics need to be about 6 feet away, a couple of feet above the strings, one on the player end and one near the opposite end. You are looking for a balanced sound in low to high frequencies. Rock piano usually has more hammer sound to it so you can get closer to the strings. An XY configuration over the bridge area or split mics to cover the lows and highs works well.
What are YOUR favorite piano recording techniques?