Pick a Spot
Everyone looks for ways to change their tone. Whether they're trying to emulate the sound of a great player or they're looking for new sounds, most players look to different guitars and amps for tone changes. In reality, guitars and amps have little to do with your tone; it originates from your hands.
Have you ever noticed that, while Eddie Van Halen has changed guitars and amps over the course of his life, he still sounds the same? Although string gauge, string height, and pick can make some difference, the sound of his guitar has more to do with the way he approaches the instrument than the equipment he uses.
The most immediate tone change you can get comes from moving the location of your pick. The guitar, especially the acoustic guitar, has a remarkable range of colors that you can create just by changing where you pick. Most players tend to pick halfway between the end of the neck and the bridge. This is a nice place to pick because it gives you an excellent round sound for most playing situations. But move away from this central spot and you alter your tone dramatically.
Experiment with pick placement for some dramatic tone changes. If you pick closer to the bridge, you'll get a more metallic sound; as you approach the fingerboard, you'll get a very sweet, syrupy sound. Playing closer to the neck can help an appealing chordal passage sound more delicate. Playing up near the bridge can help to emphasize a lead part or an important melody that needs to stand out.
On an electric guitar, you'll get some changes in tone by changing where you pick, but the effect will be much more pronounced on an acoustic guitar.