Many guitarists take great pride in handling their own guitar maintenance duties, tweaking every facet of their instrument's playability, sound, and setup until it's just right. I have never been one of those people. Unfortunately, I derive no satisfaction whatsoever from maintaining my own instruments. In fact, I view it as a tedious chore. I do it anyway, though, because it's not really all that difficult, and because I'm a poor musician-writer guy who can't afford to pay a professional tech every time one of my guitars needs a minor intonation or neck adjustment.
Perhaps because most common electric guitars are very simple instruments, consisting mainly of a couple of wood planks and some basic, passive electronics, most setup and maintenance requirements can be easily handled by the novice. Very few tools are needed, and typically, any mistakes made will not result in permanent damage to the guitar, and can be easily reversed. Factor in the financial advantages, and it becomes clear that there's really no reason why any player should not handle the bulk of their own maintenance and setup requirements. For those just embarking on the DIY guitar maintenance journey, I have put together a short, basic primer to get you started.
One of the nice things about doing your own maintenance is that most jobs don't require special tools. In fact, you probably already have most, or all, of the necessary tools on hand. These include a basic selection of Phillips screwdrivers (sizes 0, 1, and 2 cover the vast majority of guitar screws), a pair of wire cutters, a ruler or other suitable measurement device, 3-in-1 oil, a chromatic tuner, and perhaps a set of Allen wrenches and a string winder. These are just the required tools for basic setups on the most common guitars. Other options are available to make certain jobs easier, or for those tackling more complex adjustments or electronic maintenance.
The Fundamental Tweaks
To get most guitars in good, functional playing condition, the necessary points of adjustment will be the neck, the action at the bridge, the intonation, and the pickup height. I would suggest doing these adjustments in the order I just listed them in, particularly because if you adjust the neck and/or bridge after setting the intonation, it will cause your intonation to shift. Let's not create more work for ourselves than necessary. That leaves less time for rockin'.
A neck adjustment on electric guitars is done by means of a truss rod, which is a metal rod inside the neck that can be tightened to counteract the forces of tension put on the guitar's neck by steel strings, or conversely, loosened a bit to allow what is commonly referred to as "relief" in the neck. Many guitarists prefer a perfectly straight neck, while others prefer a little bit of relief. For instance, players that tune down and/or play with a more aggressive attack will often prefer some relief to allow the strings to vibrate without interference. If you're not sure what you prefer, shoot for getting the neck as straight as possible, and then go from there.
The truss rod is usually accessed on the headstock (where it is often covered by a small plastic plate), or at the base of the neck where it meets the body. The latter scenario is, frankly, a huge pain in the ass, and requires that the neck be removed from the guitar. You have my sympathies if your guitar is laid out in this fashion. Either way, the adjustment itself is fairly straightforward; righty-tighty, lefty-loosey. For more relief, go counterclockwise. For less relief, turn the rod clockwise. Most guitars come with the appropriate wrench to adjust the truss rod. Adjustments should be made in very small increments, such as a quarter-turn (or less) at a time, because typically very few turns will be needed to get it dialed in. After each turn, carefully evaluate your progress by eye, and by playing a little to help ferret out trouble spots. Also, truss rods can be broken if turned too far, so take great care, and if at any point the truss rod becomes stuck, just stop what you're doing immediately and take the guitar to a professional. Otherwise, you risk serious damage to the neck, which will likely not be inexpensive to repair.
When doing truss rod adjustments on my own guitar, I find that the previously described method usually gets the job done quickly and efficiently, but for players with Type A tendencies, there are much more rigorous and exacting methods. I will not get into those here, but if you're the kind that always strives for perfection, and you love taking very small measurements, then there are plenty of other places on the Internet that offer detailed directions for these more precise guitar setup operations.
Adjusting action at the bridge
Setting the string height at the bridge is very simple for most guitars. For Gibson-style Tune-O-Matic bridges, the only adjustments to make are at each end of the bridge, where you will find a little thumbwheel that screws the bridge studs down further, to lower the action, or pushes it up, to raise the action. For most standard Fender-style guitars, each saddle can be adjusted individually, usually with a tiny Allen wrench. Simply turn the pair of adjustment screws on each saddle clockwise to raise that saddle, or counterclockwise to lower it. Visually check the saddle to make sure that it's level, and that each screw has been adjusted a roughly equal amount.
As far as string height goes, both Fender and Gibson have specific recommendations. Gibson recommends a minimum 3/64” (1.16 mm) between the high E and the 15th fret, and 5/64” (1.98 mm) between the low E and the 15th fret, while Fender recommends a minimum height of 4/64” (1.6 mm) above the 17th fret. Personally, I have never taken actual measurements of the action when setting up my guitars. As with the truss rod, I find that making small adjustments to the bridge or saddle height, and then tuning up and checking my work, is my preferred method. Everyone's action preferences will be different; delicate-fingered virtuosos will probably prefer lower action, while ham-fisted bashers like myself often like slightly higher action.
Setting the intonation will likely be the most frustrating part of the setup process for the beginner, but with a little practice it becomes second nature. It is most easily and accurately accomplished with an electronic tuner of good quality (I usually use my Boss pedal tuner), so make sure to have one on hand, along with a trustworthy cable, and an appropriate screwdriver or Allen wrench for moving the position of the bridge saddles backward or forward. Also, make sure to start the process by installing a fresh set of strings. Old strings are a frequent cause of intonation difficulties, so just take them out of the equation right away.
The idea with intonation is to make sure that the exact halfway point of the string is at the twelfth fret. This insures that the guitar is (relatively speaking, anyway) in tune with itself, and that notes and chords played anywhere on the neck will sound as harmonious and in tune as possible. Begin the process by holding the guitar in a normal playing position, plugging in to your tuner, and tuning up. Check the intonation of the first string by playing it open, or plucking its 12th fret harmonic, and then fretting the note at the twelfth fret of that same string. If both notes register the same on your tuner, all is well. Move on to the next string. However, if the note at the 12th fret is sharp or flat compared to the open or harmonic note, some adjustments will need to be made. A handy rule for remembering which direction the saddle should go in is, "fret, flat, forward." This means that if the fretted note is flat, move the saddle forward, towards the pickups. If it is sharp, move the saddle backwards. Remember to make small adjustments, re-tune, and check your work often. Keep at it until the open note and the fretted note register the same on your tuner. Once you have achieved optimum intonation on the first string, tune up again, and repeat the process for all of the other strings.
Pickup height and nut work
The final elements of the basic setup to address are pickup height, and perhaps nut lubrication. Setting pickup height is easy; just grab an appropriately sized Phillips head screwdriver, and turn the pickup height adjustment screws clockwise to get the pickups closer to the strings, and counter-clockwise to move them further away. Every guitar manufacturer has a recommended distance that the pickups should be from the strings, and pickup manufacturers typically have recommendations as well. Following these recommendations will give you a good place to start, but don't be afraid to experiment. Some players prefer the sound of the pickups closer to the strings, and some prefer them further away. It will likely vary quite a bit between various kinds of guitars and pickups. Moving them closer will usually result in more bass and output, while further away will probably sound clearer and more mellow. For example, on a Les Paul-style guitar, many players like the bridge pickup closer to the strings for more punch and body, while preferring the neck pickup further away, to enhance clarity and high-end harmonics. Use your ears and experiment, and you shouldn't have much trouble finding an ideal spot.
Regarding the nut, many will benefit from a bit of regular lubrication. If you sometimes hear that annoying "tink" sound when tuning up, then you probably have a string that is binding at the nut. If the problem is serious, then you might need a nut filing job (which should probably be left to a professional), but most likely a very small drop of nut lube applied every so often will fix the problem. There are oils marketed specifically for this purpose, but I have found that regular old 3-in-1 oil works as well as anything else.
The benefits of DIY
Though it might be tedious and challenging at first, doing one's own guitar setup work can be very rewarding. The main reward is in money and time saved, as most guitars require fairly regular tweaks. Intonation can shift over time, or if you switch to a different size or brand of strings, and weather and atmospheric humidity changes can alter the relief of the neck. If you have to make an appointment with a guitar tech every time something like this occurs, the bills and time spent can add up. Doing it yourself also allows for a greater degree of personalization, letting you tinker and experiment until your ideal guitar setup is achieved.