By far the most crucial aspect of recording acoustic guitars well are the microphones used to record them. For instance a dynamic vocal mic will neither be sensitive enough to handle the instrument's relatively small volume, nor able to cope with the fretboard's entire frequency range. Go for a good quality capacitor (condenser) microphone every time.
Tip: record in an environment that sounds good to start with. Ever tried the bathroom? You might get a great result from those super sound-reflecting tiles. Also using a room with a wooden floor and walls can sound very nice when recording acoustic guitars, electric guitars are different although most instruments sound better in wooden rooms.
The next most important thing is to position your mics correctly. I will list two ways that are used quite often in recording, nothing beats experimenting different positions with headphones on. A 30 foot extension cable for headphones come sin handy when doing this.
Position your mic about 24 inches (0.6m) from the neck to body join. The idea behind placing the head of the mic a fair distance from the instrument is to be able to capture some of that resonant air emanating from the instrument. Its a common rule in recording any instrument to record at least the distance of the widest part of the instrument. ie on a guitar to body that vibrates to create the sound is about 2 feet hence the 24 inches. If you mic up the guitar inside of these 24 inches then the mic position is very critical and the smallest movement in the mic position can create a hugely different sound.
Tip: If you want your acoustic to sound right up front in your face, record in stereo. That's to say, get two good quality capacitor mics, point them across each other at roughly 90 degrees and keep their heads real close. Ben Harper, one of my favorite musicians used this trick on his WILL TO LIVE album.... You can hear his hand sliding across the frett board in stereo ! You can hear the movement of his slide in the frett noise. An article on stereo miking techniques is found here.
Another method to try is place a mic slightly off axis to the sound hole between 1" and 6" above or below the sound hole. This technique is mostly used in live sound since it will give less of the room sound and less chance of feedback in a live environment. Rolling off some bass around the 100 Hz region is nearly always needed with miking at the sound hole.
You'll know when you have succeeded when you merely have to apply minimal corrections in EQ to achieve a strong and acoustically pure result.