Free: Soundcraft Guide To Mixing

Soundcraft has a great 32 page booklet on audio mixing available here as a downloadable pdf.
they also have the same guide available as an i Phone app, but that will cost you 3 bucks.

ACOUSTiC GUiTAR
• Use the best mic that you can, preferably a condenser type.
• For a natural tone, position the mic between 12-18ins from the
guitar, aiming at where the neck joins the body.
• If recording in stereo, point a second mic towards the centre of
the neck, about 12-18ins from the instrument.
• Acoustic guitars sound best in slightly live rooms, if necessary
place a piece of acoustically reflective board beneath the player.