guitar and style dependent, of course, but....
the 12th fret thing is generally a starting point for one mic, and also just over the player's right shoulder looking down at guitar (as mentioned earlier)
can be great - guitarists can like this, as it is the perspective they hear their guitar from, via the right ear.
much more mids than the 12th fret thing, but mids are beautiful. and missing at the 12th fret.
a mic on the lower bout will get even more mids and not a lot of anything else.
i usually pick 2 mics and blend with small diaphragm mics a foot or two away. most of the time with LDC i use just one further back (2-3ft)
the equation for the exact distance is personal taste minus situational demands divided by room acoustics.
mics? most really good ones will work... +1 on the km54/56 & km84, mkh40, under rated - gefell m300 especially if there are also vocals.
LDC is fine too, U67 a fave, or 87, 414 if it is all silver or a TLII.
acoustic guitar is where inexpensive mics can sound like plastic. a good litmus test for mics.