When you go to buy a guitar, you'll have to decide which options you want.
The Cutaway
On some steel-string acoustics, you'll notice that the bottom of the body is partially cut away to allow you fingers access to the higher frets near the sound hole of the guitar. This is called "the cutaway." The cutaway makes playing solos a lot easier, because you can reach those high frets (that is, you can reach higher notes) and really make your guitar scream. But beware: The cutaway hurts the overall loudness and sound of a guitar, because there is less "open guitar" through which the air can resonate. The cutaway is generally not available on the classical guitar.
Body Type
The top of the body (the face of the guitar, and the part where the sound hole is) works like a speaker when playing, so it is an important consideration. The top of the body is generally built in two different styles:
Laminated veneer top: This type of guitar face is constructed of thin sheets of wood glued together. A laminated veneer top does not provide the best top for an acoustic, and thus is cheaper, but the sound quality is worse.
Solid top: This face is a solid piece of wood and resonates much better than a laminated veneer top. Thus, the overall sound of the guitar is louder, clearer and better. The drawback, of course, is the price. Solid tops cost a lot more than laminated veneer tops. It's up to you to determine if you think the increase in sound quality is worth the increase in price.
Guitars may have a solid top and veneer sides. This is not optimal (and correspondingly less expensive), but the overall sound quality is still better than that of a veneer top. This may be a good alternative if you want to get better sound quality than a veneer-top guitar, but don't want to shell out the money for a purely solid guitar.
Yes, acoustics also need electricity. It's hard for the people in the back row of a 30,000-seat stadium to hear you play "Blackbird" from a mile away. So modern science came up with the idea of either using a microphone or a pickup to amplify the sound of an acoustic guitar. This is not the same as an electric guitar, which has a distinctly different sound from an acoustic guitar.
There are four ways to amplify your acoustic:
Microphone: There's always the old-fashioned option of just sticking your guitar in front of a microphone. The catch is that microphones run the risk of giving feedback, and are hard to set at a good volume.
Sound-Hole Pickup: Instead, you could go for a sound-hole pickup, which is a special microphone placed in the sound hole. A pickup amplifies the sound that you produce on your guitar, then sends it via a cable to a speaker that emits the music. If you get a sound-hole pickup, make sure it can fit into your sound hole!
Piezo Pickup: This is the most popular choice for acoustic aficionados. They are versatile and extremely easy to use. You simply mount the pickup under the bridge of the guitar. (However, some people claim that the piezo pickup does not produce a realistic acoustic sound.)
Acoustic-electric guitars: Acoustic-electric guitars provide one final alternative for amplifying sound. These guitars have a built-in pickup, and usually have a graphic equalizer for fine-tuning the sound. These guitars are pricier than their brethren, and guitar connoisseurs will tell you that the pickup and equalizer detract from the body of the guitar, creating a worse acoustic sound than a pure acoustic guitar. But they're good at being loud.
Aesthetics
An often-overlooked part of searching for a guitar is how visually appealing that guitar is. After all, you're shelling out your hard-earned cash, so you might as well be happy with it. Inspect the guitar for discolorations, dents or scratches, keeping in mind that lower-end guitars are bound to have some defects--it's hard to get around them when instruments are mass-produced.
