I was going to start typing, and figured this was easier. From Reddit:
First question, can you hear the buzzing through your amp? Some fret buzz on an electric is normal, but if you can hear it through the amp then you have a problem.
Second, do you know how to set a guitar up correctly? You can’t just adjust action without affecting a slew of other things.
If you don’t know how to set up your guitar, there are plenty of good online resources, or get into your local shop and have them look at it.
If you want to do it yourself, there is an important order of operations that will help to ensure your setup is balanced and you aren’t doing a lot of redundant work. As you do more setups and get better, you can cheat a bit because you’ll have a better understanding of how each adjustment relates to everything else. This is how I go about a normal set up.
A couple thoughts first: Tune up between each step and do all measurements in playing position (not laying on it’s back). You want the guitar to be in as close to it’s normal playing state as possible so that you’re setting it up to its natural state. If you check measurements while it’s laying on it’s back, there is a chance that gravity or the weight of the instrument will be affecting what you’re measuring. If you measure in playing position, gravity and weight shouldn’t change (unless you’re playing on a different planet). Also, if you’re changing string gauges from what is currently on the guitar, you’ll probably need to do a full set up, you might even need to do a second adjustment the following day once things have had time to settle. Very little about a guitars setup is final, and to me, that’s half the fun!
Here we go:
* Fresh strings - Get them on, stretched and tuned to pitch. You’ll have to do this a couple times until stretching them only affects their tuning slightly.
New strings are an essential starting point for any good setup!
* Truss rod adjustment - Capo at the first fret (this takes the nut out of the equation) and use a finger to depress the low E at the fret where the neck meets the body (17th fret on a Les Paul for example). At halfway between (somewhere around the 7th fret), you should have a string to fret gap similar to that of a high e string (0.010" / 0.25mm) or a credit card as someone mentioned.
This image shows the different bows that are possible on your neck. If you have an up-bow (too much gap), you will need to tighten the truss rod (turn clockwise). If you have a back-bow (no gap), you will need to loosen the truss rod (turn counterclockwise). Some people want their neck to be perfectly flat but a slight relief is more common.
Don’t be afraid of your truss rod; give it an eighth to quarter turn at a time and check your measurement after each turn, it doesn’t take much to make a difference. If you can’t turn the truss rod or the nut just spins without making a difference, get the guitar into a tech. Just go slow and check your work often. If all goes well, you now have a nice even platform to adjust your action from.
* Re-tune your guitar.
* Now it’s time for the action. Keep the guitar capo’d at the first fret, you want to keep the nut out of the equation because if it’s cut poorly it will effect everything else. At the 12th fret, measure between the high e and the fret crown, you should have around 3/64" (1.19mm) gap. You can use a US dime for a rough measurement. On the bass side, measure between the low E and the 12th fret crown, you should have 5/64" (1.98mm). These measurements are a general starting place. I like my action a bit lower and drop about 1/64th on each side, maybe a bit more depending on the guitar. If you have a Tune-o-Matic bridge, you’re done! The bridge is already radius matched to the fretboard, and any adjustment you make to the bass/treble sides will adjust the full bridge. If you have a bridge with individual saddle adjustments, you’re going to need some way to ensure that each string is adjusted to match the neck radius.Stewmac makes these or you can make your own as long as it matches your guitars neck radius. Put the gauge down onto the correctly adjusted outside strings and raise/lower the inside strings until they all sit flush along the radius gauge.
* Re-tune your guitar
* Now the nut. This is probably the toughest thing to get right for amateurs because it requires specific tools, a good eye and feel for what is right, and a lot of patience.
For me, I like to think of the nut as a fretted note, no different than any other fret down the neck. It’s technically the 0 fret. So if you fret at the 2nd with your index finger, and then fret the 3rd with your middle, you should be able to see how much movement/action is required to fret a note. Now take your finger off of the 2nd fret and press down on the 1st. Is there more action until the note frets cleanly? Fret slots need to be deeper. Is there less action? The slots are too deep and the nut will need to be shimmed, repaired, or replaced. I like working on guitars and own a bunch so I’ve spent the money on a set of nut files and blanks. If you don’t want to go that deep, just get your guitar into a tech and they should be able to replace it for somewhere around $60.
* Re-tune the guitar and give it a couple of strums. Fret some notes up and down the fretboard. All good? Is there buzzing still? Can you hear it through the amp? Does the guitar feel good to play? Now is the time to go back and check your measurements and adjust anything to your preference.
* Re-tune your guitar and intonate the 12th fret harmonic against the fretted note. Is the fretted note higher than the harmonic? Lengthen the string by moving the saddle back towards the tailpiece (or strap button if you don’t have a tailpiece). Is the fretted note lower than the harmonic? Shorten the string by moving the saddle towards the neck. You should probably be using a good strobe tuner for intonation, but I’ve been using my Sonic Research Turbo Tuner pedal for years and I feel like it does a good enough job.
Most of the time in my experience, fret buzz has come from a neck with no or not enough relief. Second place is a nut that’s poorly cut or worn, and finally action (saddle height). If all else fails, you totally botch it, or you’re not interested in doing it yourself, you can always pay to have it fixed. It’s a tool, not a baby.
There are plenty of good vids online that will help you with each individual step, I like the tutorials on the Elixer site because they’re close to how I was taught.