Many beginning or even intermediate guitarists are unaware that their guitar should be "set up". The adjustments described in the adjustment subsections below (along with restringing and tuning) are called a "set up".
= What difference does a set up make? =
When a guitar is set up properly:
the guitar will feel and sound its best
all the strings will sound with exactly the notes they are supposed to
all notes will sound correct when played at each fret up and down the neck
the guitar will be as easy as possible to play
strings will break less frequently.If a guitar plays easily and sounds its best then it's easy for the player to feel successful.
When a guitar is not set up properly:
the guitar may not feel or sound quite right
some notes may sound correct while some others may sound sharp or flat
the guitar may be difficult to play
strings will break more often
damage to the instrument could be incurred unwittingly by the player
== When to Set Up? ==
When a guitar is brand new and fresh from the factory it may or may not have had these adjustments done. As a rule, a guitar should be set up when first purchased (used or new) and again when switching string gauges. Consider getting a set up anytime the guitar sounds or feels different than it used to. Perhaps after a guitar travels (altitude changes, pressure changes, and humidity can affect the wood in the guitar) and just like changing oil in a car it is a good idea to get a set up every now and then for maintenance purposes (perhaps twice a year).
Poor set up may be obvious to a player or it might not. In some cases the guitar may be unplayable because it hasn't been set up. A maladjusted guitar can cause strange quirks, for instance frets near the bottom of the neck being too sharp, or can even cause damage (e.g., by using .012 gauge strings on a nut designed for .009 strings, and the tension messes up the nut), and it can easily frustrate the player when their playing is perfectly correct yet things still don't sound right.
In particular if your guitar ever becomes difficult for you to play, a set up will probably help.
It is not absolutely required to set up a guitar, but it is nonetheless a good idea, especially if the guitar is to be taken to the stage. Some people never get their guitar set up. Some get their guitar set up even when nothing previously seemed wrong with it, then find such a dramatic change in the guitar's playability and sound that they wish they had set it up sooner.
== How to get a Set Up ==
These adjustments should generally be done by a professional, qualified repair person. They require precision instruments, some hard to find tools, a steady hand, quite a bit of time and know-how.
Virtually all musical instrument stores will be able to perform a professional set up. Some will do the job better than others. Call a local music store and ask them "Do you do set ups for electric (or acoustic) guitars and how much would you charge?". Getting a set up will probably cost from $30 to $75 USD.
= Adjustments =
== Adjusting action at the bridge ==
This is a simple adjustment that can usually be performed without professional assistance. The bridge saddles should be lowered if the string action is too high, that is, the strings are too far up off the fretboard. In some cases it may be desirable to raise the saddles for a higher string action.
Most electric guitars have two small screws on the saddle which can be used to raise or lower the saddle. Some saddles have screws that can be rotated using the fingers; others require an allen key. Lower the saddles too much and the strings might rattle against certain frets (this may or may not be inconsequential on an electric guitar; listen through an amplifier). In more extreme cases, pressing a string against one fret might actually fret the string against a different fret, usually the one under the intended one. In both cases, filing the frets might alleviate the problem if the saddle really should be that low. Otherwise, simply raising the saddle a small amount on the side with the problem should be fine.
== Filing frets ==
The frets go with the shape (or contour) of the neck radius (9, 12", 16", etc.) Frets can determine how the notes on your guitar sound (i.e. intonation) and over time and use playing a fretted instrument the frets will begin to wear out by either changing the shape of the crowns (the top of the frets, and they are changed by being flattened out or mis-shaped)or the frets will begin to leave their slots. Fret work should be done by someone with experience doing this kind of job because this is a job that can lead to worse problems on your guitar such as your tonation being worse, action may be higher, strings may buzz out, and it may require that multiple frets be replaced or further repaired. Frets come in a variety of sizes as well making them each different to work on and there are special tools available to do this line of work but many are expensive and without proper training may not be used correctly.
== Filing the nut ==
Filing the nut should only be done by a qualified repair person and is used to reduce pressure at the nut to allow a heavier gauge of strings to be used. It may not be necessary if the new strings are detuned lower (e.g., when switching from .009's to .010's, the nut will need no adjustment if the guitar is tuned to Eb-Ab-Db-Gb-Bb-Eb instead of E-A-D-G-B-E).
== Neck/truss rod adjustment ==
This particular adjustment has been known to ruin guitars when performed incorrectly, so here referral to a professional repair person is highly recommended. A guitar will need a truss rod adjustment if the neck is not straight. One way to check the straightness of the neck is to play 12th and 19th harmonics on the low and high strings. After sounding each harmonic, fret the note there and play it again: it should be exactly the same pitch. If it is not, the neck may be in need of adjustment. However, this may be indicative of an intonation problem as well, which can be fixed without the aid of a repair person; see below. If adjusting the intonation does nothing for you, give the guitar to a repair person.
== Adjusting intonation ==
You may notice each string on the bridge sits in a "saddle". Depending on your setup, you might notice the saddles may be in different positions: some might be pushed forward and others might be pushed back, sometimes slightly. The positioning of the saddle effectively changes the length of the vibrating string. Tune the guitar to concert pitch with the aid of an electronic tuner, making sure the open strings are perfectly in tune. Play the 9th and 12th fret harmonics, then play the fretted notes. If the fretted notes are sharp, the string is too short and the saddle needs to be pushed back toward the base of the bridge. If the note is flat, the string is too long and the saddle needs to be pushed up toward the nut. Repeat this procedure for each string. Adjusting the intonation should be done every few months or at least twice a year (Every six months interval).