When micing any acoustic guitar, you need first to decide whether you are going to record in mono or stereo. Recording in mono will usually require you to double the track later. Recording in stereo may require some panning adjustments. Certain types of microphones capture certain aspects of sound depending on the size, shape, and strings of the guitar. One would typically use a condenser microphone on an acoustic guitar as the output of an acoustic instrument does not generally have a very loud SPL (sound pressure level).
Nylon string guitars are generally quieter than steel string guitars and, therefore, may require a more precise microphone such as the Neumann KM84 or Audio Technica AT4051B’s. Due to the type of guitar music typically played on a nylon string guitar, it is usually wisest to use two microphones. Because steel string guitars tend to be much “louder,” a single larger diaphragm microphone will suffice, such as a Neumann U87 or an AKG 414 (also great as a spaced pair).
In general, you want to point the microphone about 6-9 inches from the sound hole as a starting spot. Feel free to move the microphone around until you get the sound you are looking for. In ProTools, make sure your pan is set to dead center, so you are able to listen to the guitar in both speakers for a more accurate sound.
To double the guitar, you will need to record another pass on a second Pro Tools/Logic track. This time, you will use your panning to identify time discrepancies by panning your recorded guitar into one speaker and the active recording into the other. The blend of the two tracks should ideally sound like one guitar with a very full sound.
Another way to mic an acoustic guitar is with a spaced pair. In a spaced pair, one microphone should be pointed roughly at the twelfth fret of the guitar, with the other pointing roughly at the sound hole. Again, use your panning to pan each microphone into a separate speaker so you can hear the blend of the guitar and each microphone in stereo sound.