Take a look at the strings of your guitar, what sort of shape are they in? Are they discolored? Rusty? Are all six strings present and accounted for? If you answered no to any of these questions, or if it's been several months since you put new strings on your guitar, it's time for a string change. New strings make your guitar sound brighter, and generally make it easier to play.
How Often Should I Change My Strings? Just like brake pads on a car, guitar strings wear out with use. Old guitar strings often behave badly - they'll lose tuning more quickly, sound less "bright", and give you problems with intonation. Old guitar strings also break, often during the most inopportune moment. Here you can find just about every type and gauge of string you'll ever need - from all your favourite manufacturers: Ernie Ball, Elixir, D'addario, Rotosound, Dunlop and more.