In my experience every upright piano is a bit different--if ever there was a case for trying positions and listening, this is it.
First of, I much prefer to record pianos in stereo so we'll be talking two microphones. Unless you want to re-arrange your room (and break your back) we can discount putting the mics behind the piano which can be a good location.
Therefore, let's try having the top lid open and miking from there.
I'd be using small diaphram condensers (if only because of the need to get them into small spaces) and probably have one over the bass strings and one over the treble end, each about a quarter to a third of the way in from the sides. I'd place the mics so the capsules were just inside the case of the piano. I find this give a natural sound with just enough of the hammer attack to sound right. However, moving the mics even an inch or two can give a big difference in the sound, so play a bit before you record.
That said, there are all sorts of different ideas about placement, each with a slightly different sound.
THIS SITE has a good diagram (from Shure) down near the bottom which lists at least six options and gives the pros and cons of each.
Good luck! I wish MY son had some musical ability!
Bob
