Good resources:

http://www.youtube.com/watch?v=x8dpk3t1TdI

http://www.projectguitar.com/tut/pro1.htm

By G String

What exactly's the problem? High action? Sharper notes as you ascend the fretboard?

If you adjust the truss you're going to have to also adjust bridge height and intonation. Let's say both action and intonation are out of line. Before you begin make sure you have your preferred string gauge choice already on the guitar.

First thing to do is adjust the truss. You're going to want the neck as straight as possible when all the strings are tuned to pitch, with just a little bit of bow. Be very, very careful when twisting the truss clockwise. Counterclockwise bows the neck. Line your eye up with the neck, facing parallel to your line of vision, to check for this.

After you do that, adjust bridge height which corresponds to how high the strings are off the neck. TOM style bridges are a pain in the ass to adjust, because you have to detune each string to bring the bridge up/down. Strat or Tele style being the easiest because you can stick in and twist the hex with strings tuned to pitch. This step usually takes me the longest because my last few guitar acquisitions have TOM bridges.

Last thing to do is intonation. Grab a good chromatic tuner and sit down with your guitar. Start by tuning each string to pitch. Play ay a harmonic at fret 12 on each string, and then play a fretted 12th fret. Both a string's harmonic 12th and a fretted 12th fret should be in tune with each other. If the 12th fretted note is SHARP, bring the saddle away from the neck. If the 12th fretted note is FLAT (rare, IME), bring the saddle TOWARDS the neck.

Keep in mind any time you alter tuning (drop 1/2 step) or switch string gauge (9s to 10s), you may need to adjust truss, action, and intonation again. The first time it's pretty arduous but once you do it more than once it's not that tough. It just takes a while, but is made MUCH easier when you know what height of action you want and you have a good chromatic tuner.

By Breakfastime

When you're sighting down the length of the neck checking for relief in the fretboard, hold the guitar up to a light source, with the headstock pointing towards the light. As you get the length of fingerboard in sight (peering down the neck from the bridge area) press the low E string against the very last fret (the highest fret), as if you were fingering that note.
Now you have a 'straightedge' to judge against. The string becomes your straight line, and you can see how much relief is in the neck, and where.


Also, don't tighten the trussrod without first loosening it a little. Just don't. Loosen that thing maybe a half turn (always bear in mind how much you are turning the thing, and don't tighten it more than maybe a quarter turn at a time)
Loosen the nut, and you might hear some little sounds emitting from under the fretboard, little groans/squeaks.. that's okay. Now you can re-tighten the ting...but don't just start tightening it up. A broken trussrod is an expensive fix.

Also, the adjustment will have something of an immediate effect, but it will also sort of 'settle in' and you will notice subtle changes over the next day or so.

Just don't try to fix it in one swoop. It's better to make a couple of slight adjustments than one big twist.