Select the right guitar. There are many variables and possibilities to consider. Steel strings carry better than nylon strings. Chris Bozung of CB Custom Guitars points out that thick-waisted guitar bodies (those that do not narrow drastically in the middle) will produce a bigger sound. Tighter-waisted bodies tend to produce “a more focused sound with very solid overtones.” Larger-bodied guitars have greater volume capability. Among the less expensive woods, Englemann spruce offers quicker response and greater volume than the more commonly used Sitka spruce. The metal-bodied National guitar is amplified by built-in speaker cones called resonators that produce a very wide dynamic range and a volume that far surpasses all wood-bodied guitars. Also, resonator guitars with speaker cones built into a wood body produce more sound than all-wood acoustic guitars. The 12-string guitar puts out more volume and a “fuller” sound than a standard guitar with six strings.
Use the PA system for the right mix. If a PA system is available, an acoustic guitar can be put on a microphone and amplified through the system. Systems tend to have more than one input, making it easy to mic both voice and guitar. A more common problem in live performance is being sure that the vocal can be heard above the guitar. In that case, the solution is to simply mic the voice and go with the guitar’s natural unamplified sound. If you don’t have a PA available, modify your playing and singing to get their volumes to mix effectively.
Emphasize chords. If you’re in an environment where you're sure the guitar is being heard, emphasize chords in your solo breaks. Chords carry better and make an impact. There’s no point in doing sophisticated single-note picking that people have to strain to hear. Think of where you want your solos to go and figure out how to get them there with whole chords, partial chords and arpeggiated chords rather than using a single-note style.