Does your guitar sound like garbage?
There are several reasons why your guitar sounds bad, but the most common one is the tuning of your guitar in the higher positions of guitar's fretboard.
The rule says:
If you play an unfretted string (fret 0) and then strum the note on 12th fret of the same string, you should get the same tone, but played one octave higher. So, if you play the E string, fretting the 12th position should return E, an octave higher.
To figure out if your guitar matches this criteria, tune the string in the Digital Guitar Tuner and then play the 12th fret on the same string. If the ray stays at the center, everything is OK. If it moves away from the center, you might want to attempt making some adjustements to your guitar.
And what kind of adjustments?
The solution is different for electric and acoustic guitars.
On a six-string electric guitar, there are six little screws (see picture below) on the bridge, one for each string. Adjusting these screws changes the tuning of your guitar.
So, if you have electric guitar, you'll manage it this way:
1. Tune the string to match the desired frequency (using DGT or
other guitar tuner)
2. Check the status of the 12th fret. (if it plays the same tone)
3. If the result is unacceptable, turn the proper screw with screwdriver. (just slightly)
4. Repeat from step 1 until it's OK. (IT IS neccessary to tune the unfretted string once again!)
Remark: You will notice the proper direction of turning the screw by comparing the results. After turning the screw and retuning, if the ray appears to be more near the center, you are turning the screw in the correct direction.
On acoustic guitars there are no screws on the bridge, there is only one screw located inside the body of the guitar, directly at the end of the neck (see picture below). With this screw you can adjust the tension of guitar's neck. This is not to be done with standard screwdriver, but using a special hexagonal key. (you should have bought it with your guitar in most cases)
The adjustment procedure is somewhat more delicate than in the case of electric guitars, you are to adjust the guitar's truss rod, a metal rod which counteracts the pull of the strings.
By adjusting the rod's tension, you can often cure tonal problems of your guitar. In ideal case, it should make the guitar's neck perfectly straight.