Few things make me happier than a great song played on a fine acoustic guitar.  The shimmer of the strings and the resonance of the body fill the room and warm my heart.  I’m most definitely an electric player first and foremost, but there’s just something fundamentally satisfying about playing a well-built acoustic.  This is probably why I used to get so frustrated when recording the acoustic; the sound I got on “tape” was never as good as the one I heard in the room.  Always thinner, lacking in body, and often requiring gobs of post-processing to sound halfway decent.
Eventually I learned that it’s not all that difficult to get a nice-sounding acoustic guitar recording, but you do need to know a few key things.  The first is which mic (or mics-plural, if you’re so inclined) to use. The second is where to place these mics, which is not always obvious. The third is what sort of signal processing is a good idea on acoustic tracks. There’s also a couple of rather important issues to consider: the guitar itself, and the role it will play in your mix.
Before You Start
There is one question that will drive all other acoustic guitar recording decisions: is this guitar the primary instrument in your song, or is it going to be mixed in with plenty of other stuff? The reason this question is important is it tells us how much “space” the guitar will take up in the mix, which in turn dictates how “spacious” it needs to be when we record it.  If the acoustic guitar is the featured instrument, or one of a few, we will need it to fill up a lot of the mix. If it’s just part of the background, it’s probably okay to be a bit more minimalist when recording.
The guitar itself is also a big factor. Acoustic guitars vary a great deal in volume, projection, frequency emphasis, and sustain. Understanding your guitar’s specific characteristics is essential to properly recording it.
Recording With One Microphone
The basic way to record an acoustic guitar is the basic way to record anything: put a mic in front of it. For an acoustic part that is a smaller factor in the mix, one mic will be plenty.
A good general choice for a steel string acoustic guitar is a medium or large diaphragm condenser mic with a side address cardioid pickup pattern. This is the same kind of mic you might use for vocals, but the important difference is that your acoustic guitar is putting out a much wider frequency range than a human voice. Most high-quality large diaphragm condensers will be just fine. My personal choice is a Neumann TLM 103 because of its overall warmth, detail, and excellent high frequency reproduction. You definitely don’t need something as expensive to do a good job though. I’ve also had excellent results from budget condensers, such as the Audio Technica AT2020 or the Rode NT1.
You may be tempted to cram that mic as close to the sound hole as possible, because it’s a hole for sound to come out of, right? Well, sort of, but the facts are the sound coming out of the sound hole will tend to be a bit “woofy” due to all the air being pushed in and out of there, and the entire vibrating length of the string is producing sound, not just that hole.  The industry standard placement for your primary mic is between 2 and 3 feet away, pointed at the 12th fret.  This will produce a balanced, neutral tone that incorporates as much of the string and body as possible without getting too distant.  As with electric guitar pickups, moving the mic closer to the bridge will bring out more treble frequencies, so if that’s what your guitar part demands go ahead and move that mic a little closer to the bridge (but keep it 2-3 feet from the front of the guitar).
My last important tip with the single mic: try not to move around too much, or really, at all.  This is easier said than done for some people, so if you’re a player who tends to move a lot while performing you may want to back the mic up and turn up the preamp gain.  This can help you catch everything no matter how much you wiggle and wobble, but it might also increase noise and other bad things you don’t want.
Adding Another Mic

The AT2020 and AT2021 from Audio Technica make a great pair for acoustic guitar recording, and they are available as a cost-effective kit.

A good condenser on its own will be more than enough to capture a guitar that will sit back in the mix, but for an acoustic to really fill up the sonic space a second mic is a great idea. There are plenty of ways to use two mics on an acoustic; I will cover a couple of them here.
If you have a nice-sounding room, having a room mic can be very cool. You will want another medium or large diaphragm condenser positioned at least six feet from the guitar, but not too close to the walls. This will provide a natural reverb sound that can be blended into the mix in moderation.
The most common second mic, however, is a pencil condenser. I have experience with two positions for a pencil: aimed at the guitar at a 45 degree angle to the top (also known as “off-axis placement”), and my personal favourite, positioned near the headstock and pointing down the neck. If you want to add some more shimmer and detail to what your primary mic is already giving you, this is a great way to capture that.
There is always one caveat when using two or more mics: you have to watch out for phase cancellation.  Two mics are in phase when the peaks and troughs of the sound wave are hitting them at exactly the same time.  Mics that are out of phase can cancel each other out and work against each other.  The simple way to check if your mics are in phase is to mute one of them and compare.  If the one mic by itself sounds “fuller” and louder than the two mics together, they are probably out of phase.  Try moving one of the mics a short distance (no more than six inches) away from the guitar and compare again.
These are not the only ways to record acoustic guitar.  There are many options for mic choice, mic placement, and even direct recording using the guitar’s pickup.  Like anything else when it comes to tone, there is no harm in experimenting and figuring out what works for you.  If you do have a winning strategy for perfect acoustic guitar tone, please tell us about it in the comments.