The same guitar can sound completely different in the hands of two different players, and this is especially true of the acoustic guitar. Two guitarists playing the same part will often treat it very differently. For example, an A barre chord is very different both musically and sonically, from an open A chord. Many other factors also come into play - the difference between picking and strumming, plectrum and fingernails, standard and open tunings, the playing distance from the bridge
The choice of guitar can make a big difference too. The term acoustic guitar covers many different types of instrument from huge folk dreadnoughts to small-bodied parlour guitars, and twelve-string steel-strung to nylon-strung classical guitars.
A well played and well made guitar will often shine even with indifferent mics - even the best microphones cannot improve the sound of a poor guitar though, or in other words, you cant polish a ****, as somebody wise once said! Of course, the acoustic guitar is not always especially prominent in the mix cheaper instruments generally sound fine for percussive padding, while solo guitar parts are usually much more exposed, which demands quality.
This can have a considerable impact on the recorded sound of acoustic instruments - a small carpeted room with upholstered furniture sounds completely different from an empty hallway with a parquet floor. Acoustic instruments tend to sound best in rooms that are neither completely dead nor excessively reverberant, but somewhere between the two. Of course your choice and positioning of microphones will also have a big effect on the amount of room sound picked up, versus the direct sound of the instrument. If you have a choice of rooms, or a choice of furnishings and floor coverings, experimenting with them will generally represent time well spent.
As obvious as it may sound, accurate tuning is essential. While vibrato and bends often serve to mask electric guitar tuning errors, acoustic chords can sound either delightful or painful depending on whether the instrument is accurately tuned, and tuning errors are compounded by the common practice of double-tracking. An electronic tuner is invaluable even the best ears get tired during long recording sessions.
The tone of an acoustic guitar can be drastically affected by old or tarnished strings in fact, many session players change their strings before a session as a matter of routine. The cost of this can be reduced by buying sets of strings in packs of ten or more. Modern coated strings maintain their brightness for much longer, and although they are more expensive, they do save having to change strings as frequently.