Guitar Doesn't Produce a Full Sound
The guitar doesn't sound like it used to; its tones are lacking
The guitar strings have been worn and need replacing. (Some musicians try boiling their strings here)
Guitar Goes Out of Tune Often
It seems that you're always having to tune the strings
Old or New Strings
When you restring your guitar, it will take some time and playing before new strings will hold the tune as well as the old strings. If the strings are not new and going out of tune, it is time to change them. As time wears the strings, they bend more easily and go out of tune more often.
Guitar Makes a Buzzing Sound
One or more frets in particular make a ringing, buzzing sound when played
The reason a certain fret consistently produces a buzzing sound is because the distance between the string and the neck is too small. This distance is known as the action of the guitar. You are able to adjust the action by tightening or loosening the truss rod that runs through the neck of the guitar. You can adjust the truss rod at the head of your guitar with a hexagonal Allen key.
Strings Float Too Far Above the Neck
The vertical distance between the strings and the neck is more than it used to be
The distance between the strings and the neck, the action, can be reduced by accessing the truss rod that goes through the neck of your guitar. You are able to adjust the action by tightening or loosening the truss rod at the head of your guitar with a hexagonal Allen key.