As you can probably imagine, multi-mic rigs can quickly become horribly time-consuming to set up successfully, and you must consider lots of additional issues such as phase. That said, there are a couple of established dual mic configurations that aren’t too much of a burden and sound fantastic.
Spaced pair (A/B) uses two mics in separate positions, often a small diaphragm condenser at the 12th fret and a large diaphragm condenser at the bridge. The small diaphragm condenser will pick up a clear, transparent rendition, while the large diaphragm is there to add body, ambience and warmth. Done right, the result will sound huge.
Just make sure you set up each mic individually first before playing with the stereo mix or you risk losing yourself in hours of sonic befuddlement.
A coincidental pair looks to achieve similar results but this time the mics are stacked one on top of the other, aimed 90 degrees apart in a V formation. The 12th fret is a good place to start, so that one is picking up clarity from the neck while the other is finding richness from the body. Adjust left/right and back/forth until you find the sweet spot. The advantage of a coincidental pair over a spaced pair is that you’re far less likely to suffer phase cancellation issues.
Finally, before you press the big red record button, or pick your first notes in front of a live audience, make sure your guitar is in tune. It’s so common to spend hours on setting up sophisticated mic placements, only to forget the basics.