Firstly, no matter if the guitar is new, old or straight out of the box, it still needs adjustments to serve you the best. Let's take a look at some of the more important factors to set up your guitar correctly. A good idea would be to make a small scheme of what's to be adjusted. If you're not fully aware of what's to be done then read on, we'll find the problem and fix it.
1. The Truss RodThe truss rod adjustment will be necessary if the neck of your guitar has been bent or not properly adjusted from the manufacturer. This is not always to be seen with the naked eye, therefore you can use this trick to check if you neck needs adjustment.
Put a capo on the 1st fret, right on top of the 1st fret, then take your finger and put it on the fret where the neck meets the body, that’s usually on the 17th fret, then take a small business card, roughly between 0,1 mm - 0,3 mm, put it in between the neck and the string, around the 8th or 9th fret, see if the business card lightly touches the string of if the business card lifts up the string. If the string lifts up, when the business card is in between the neck and the string, then your truss rod needs adjustment. But, this is only to be done if the business card lifts up the string more than 0,3 mm. If the gap is in between the 0,1 mm - 0,3 mm, no adjustment is needed. Most electric guitars are often made with a slight curve on the neck.
Important: A good idea would be to set up the action, saddle and bridge height first. Read below.
2. Action, Saddle & Bridge HeightThe saddle & bridge height is closely combined with the action of your guitar, the height of your strings. If the saddle and bridge is set too low, then the guitar strings won't be able to sustain the tones and the sound of the guitar will sound buzzing and flat. This is where the string height comes in handy, the action. By adjusting the action of your guitar the strings will be able to sustain all tones played on the frets and sound natural and smooth.
Your guitar strings needs to be set at a certain measurement: the low E string at 3/32th, 2,38 mm, and the high e string at 2/32th, 1,57 mm. This is measured at the 12th fret, right on top of the fret and to the bottom of the string. If the string is too high, or too low, then the saddle and bridge needs adjustments. This time you take your screwdriver and turn the two big screws on the bridge and afterwords the two smaller screws on the saddle. By raising those will make the guitar strings able to sound and ring out.
3. Pickup HeightThe pickup height is important to check and adjust, this gives you the very best of your pickups. When pickups aren't adjusted correctly the pickup output will be filled with overtones and unpleasant sounds. A way to adjust this is to get your shooting canvas and measure the height of your guitar's pickups. When I did this on my guitar I didn't quite know the right height, but I searched the internet and I found a good height.
The measurement I used was 3/16th, 4,76 mm. This is measured from the top of the pickup to the bottom of the string. This measurement will set your pickups right. Measurement can vary, but this will work for many guitars.
4. IntonationThe intonation is the overall tuning of your guitar's strings. If the intonation isn't set up correctly the guitar won't stay and play in tune.
Every guitar needs intonation adjustments at some point along the way. I would recommend you to check the intonation every time you change your guitar strings. By doing so your guitar will always be at its best.
The way the intonation is set is by doing so: get a tuner, tune all strings to pitch, play the string open, see if it's in pitch, afterward fret the 12th fret of the string you're intonating, and check it's in tune too. Remember, by fretting the 12th fret means that you're an octave higher than the open string. If the string isn't in tune when the 12th fret is fretted, then the string's intonation needs to be properly set.
Now it's time to get out your screwdriver out, either a flat-headed or a star-shaped one, then you go to the bottom of the bridge and find the little screw matching the string you're adjusting. Then you need to turn the screw 'till the string is in tune. Remember, after every adjustment the string needs to be tuned to pitch again.
Got any questions? Feel free to submit them in the comments section below, I'll be happy to help you out.