The "over the shoulder" thing works really well with drums and can work with a variety of other instruments except that you can end up with a bit more of "the room" in the mic that you may want.
What is happening when you put a mic 'over the shoulder' is that the mic is hearing pretty much what the ear is hearing... except that the ear is able to distinguish between reflections as distinct events and a microphone does not have that capability.
There is this phenomenon called the "Haas Effect" which states that human hearing will incorporate reflected signals under 19ms as part of the original sound and reflected signals over 19ms as distinct 'echos'. The ear while making this determination will separate direct from reflected sound, a microphone can not make this distinction which will often give your audio a more distant character than you will often want for things like an acoustic guitar sound.
What I generally recommend for things like acoustic guitar sounds where you're looking for some added depth to the tone is to mic the guitar with two mics. The first I will generally put about a foot off the 12th fret aimed back at the guitar's soundhole. For a slightly darker tone aim the mic more toward the bass strings, for a slightly brighter tone aim the mic more toward the treble strings.
To add the depth from a second mic one of my current favorite techniques is to use an omni pattern mic aimed at the bridge of the guitar about 6-12" in front of the guitar aimed up from a short stand around the player's feet. You may need to put the stand on some foam rubber or in a shock mount if the player taps their feet while playing.
My current favorite microphone for this technique is the
T.H.E. Audio KP-6M (sorry about the link back to the M-A site, I couldn't find the MFG's website) as it sounds very natural and usually very 'rich'.
Once you have the two mics set up on the guitar check them in "one speaker mono" to listen for phase anomolies between the two mics. My usual method for placement is to get the mic off the 12th fret doing the lion's share of the work and move the omni mic by the player's feet until you get both the degree of clarity you're trying to achieve with the recording as well as the depth you're trying to achieve for the overall tone of the instrument.
Best of luck with all you do.