Acoustic guitars are one of the most dynamic and expressive instruments used in modern music. They have a broad frequency range covering almost the entire audible spectrum. The instrument can serve many different roles in an arrangement as a harmonic, melodic, or percussive element. All of these factors will affect how you approach both the recording and mixing acoustic guitars.
The first thing to do is think about its role in the song/mix. Is the guitar the main harmonic instrument? Is it supposed to enhance or thicken other harmonic instruments like electric guitars? Is it enhancing the melody, playing arpeggios or single notes? Is it a percussive element more like a shaker just to fill out the rhythm section? Figure out the goal, then you can begin processing.