An electric guitar can buzz for any number of reasons. The most common reason for electric guitar string buzzing is improper setup. The action might be too low or the neck might have too little or too much relief. These problems can be fixed quite easily with a proper electric guitar set up. Personally, I hate it when my strings buzz. It is one of the most annoying things in the world; however, I like extremely low action. When I set up one of my guitars, I have to walk the fine line between string buzzing and low action. But before we go through the hassle of completely setting up your guitar, we should try to diagnose what is the cause of the buzzing. There are reasons for fret buzzing that a setup will not fix. Let's try to figure out what is wrong with your guitar before we do any work.
If your guitar buzzes when you play an open string and does not buzz when you play any fretted note, you have a problem with your nut. When you play a fretted note, it eliminates the nut problem with the played fret, hence the no buzzing. Then after you play the open note again, the buzzing continues. Most likely your nut notches or slots are too deep. This causes the strings to sit to close to the fretboard: low action at the nut. To fix this problem, you will need to replace the nut. For more information about replacing an electric guitar nut, see the electric guitar nut replacement page.
If your guitar buzzes on a single string only on one or a few frets, i.e. the A-string on the 2nd and 3rd frets, and nowhere else on the guitar, you most likely have unlevel frets. You can tell that your frets are not level without measuring them by playing the string open and on all the fretted notes. If the buzzing is limited to those select frets, you definitely have unlevel frets. Frets can be improperly seated and stick up higher than other fret causing the lower frets to buzz. Playing a guitar with unlevel frets can really be a pain. The guitar will sound perfect until you hit the bad spot and BUZZ. It is annoying. Luckly, It is pretty easy to fix. Your frets just need to be dressed. In order to dress your frets, you will need some guitar repair tools and a place to work. For instruction on how to dress your guitar frets, please see the fret dressing page.
If your strings are buzzing on almost all of the frets, you probably have the string action set too low. The strings are basically resting on top of the frets and have no room to vibrate. The solution to this problem is to simply raise the action on the strings. To properly raise the action, you will need to do more than just raise your bridge. You should check and adjust the action completely. There are three different steps to adjusting your action: adjusting the truss rod, adjusting the action at the nut, and adjusting the action at the bridge. You can find instructions for a full action adjustment on the electric guitar action adjustment page.
If your strings only buzz on the frets when you play hard, it usually means your action needs to be raised or you need to switch to a heavier string gauge.
If your strings are still buzzing on almost all of the frets even after you adjust the action to a factory standard height, you may need to dress your frets. When frets wear down, they become flattened. The string no longer has a specific point of contact on the frets. Instead, the string sits across a flat fret or worse-- a divot in the fret. Also, all of the frets are lower than they should be. Look at your frets and see if the tops are flat rather than crowned. Another way to test whether your buzzing is because of worn frets is to play a fretted note. Then, fret the note hard and play it again. Usually the string buzz will go away when the notes are fretted excessively hard because the string is being bent against the fret and to the fretboard--thus giving the string more room to vibrate. Worn frets are pretty noticeable. You should be able to see how flat the tops of the frets are. If this is the case, you will need to dress the frets. You can find instruction about how to dress frets on the electric guitar on the fret dressing page.
There are many other specific examples of string buzzing, but the few mentioned above cover all of the common string buzzing problems. One of the only other reasons for string buzzing is a warped neck. Your guitar neck may be twisted in a certain direction causing the strings to be too close to the frets. Neck twisting usually only happens to cheap guitars. In that case, I would say it probably isn't worth fixing. It is uncommon, but nice guitar necks can twist as well. Guitar necks can be straightened, but it will take some effort.