How to adjust a truss rod

When adjusting your truss rod you are creating forward bow which adds relief to the neck. This enables the strings to pass over the upper frets without contacting them.
To check the amount of relief in a guitar neck you first need to put a capo on the first fret. Next fret the fret closest to where the neck meets the body. This is usually around the 17th or 18th fret. Now using a feeler gauge measure between the bottom of the 6th string and the top of the 6th or 7th fret. You should measure approximately .010. I usually do this on the 6th string only because it is convenient but you can use any string to measure relief.

If after measuring your relief you find you are way off it's time to do the adjustment. Be 100% sure you are using the correct tool to adjust the rod. A rod can be ruined in seconds with the wrong tool rendering the neck totally useless. If you have any doubts DON'T DO IT.
Before making any adjustments REDUCE THE STRING TENSION. Never adjust a truss rod with strings tensioned. Make adjustments in small increments taking note which direction your turning the adjuster. Re-tune the guitar and check the relief again following the procedure above. If need be repeat the whole process until you have reached an acceptable amount of relief.

Most necks will perform nicely with .010 (ten thousands). Theoretically a guitar neck can work with near zero relief but in most cases it just won't. If you prefer you can set your neck with less or more depending on your personal preference. The majority of people can not feel how much relief is in a guitar neck so .010 works the best. In cases where the guitar has fret buzz more relief must be added.

Once your finished adjusting your neck relief it's not unusual to have to go back and reset the string height. This is accomplished by setting the height of the bridge saddles.
While setting neck relief has nothing to do with string height it will change it slightly. Always set the neck relief before setting string height.