Without pretending to publish the definitive guide to guitar recording, here are a few tips on how to record an acoustic guitar with an electrostatic microphone.
The basic method for recording an acoustic guitar consists of placing a small membrane condenser mic at about 10cm from the junction of the body/neck and facing the 12th bridge. This is the “sweet spot” for the guitar: the more you move the mic towards the top or the body, the more 'bitter" the sound becomes. In any case, never position the mic directly towards the center of the body which will give you too much bass, and be very difficult to mix later on.
The hardest part is to keep the guitar player immobile during the recording process. If he moves around too much you could use the system with a mic clip which is attached to the guitar itself, like the one proposed by sE Electronics with its GM10 or DPA with the 4099G.
Note: You could also use a large membrane condenser mic or a ribbon mic and even some kinds of dynamic mics like the l’ElectroVoice N/D 967.
Note: You can also place another condenser mic at about 3 feet from the guitar to record the “ambiance”.
Note: Of course, an acoustic guitar can be recorded in stereo using a couple small membrane condenser mics, usually placed in a XY or AB position. this can be useful when there aren’t many other instruments in the arrangement (guitar/ vocals only), in order to create a natural stereo environment.