String Bending

We've learned some interesting new techniques in the past few lessons, but none that will give you as much trouble in the beginning as string bending. Bending strings is a technique used, when playing single note riffs and solos, to give the guitar a more "vocal" quality. Although it's a technique used mostly by lead guitar players, even three chord folk guitarists will call upon string bends from time to time.

Bending Technique

Bending the strings far enough to get the pitch to change (which is what we're trying to do) takes a good deal of effort. The key is to use three of your fingers to bend the string, instead of just the finger on the fret you're trying to bend. You accomplish this by placing your third finger on the fret you're trying to bend. Place your first and second fingers on the frets behind it, and exert pressure with all three fingers. Let's look at the first exercise.
  Start by fretting the note on the tenth fret of the second string, with your third finger. Your second finger should rest on the second string, ninth fret. Your first finger should rest on the second string, eighth fret. Our goal is to bend this note up one semi-tone (called a "half step"), and then return the note to it's original pitch. Play the tenth fret, then the 11th fret, so you can hear the proper pitch of the note you're trying to bend to. Then pick the note, and exert force in an upwards motion (towards you), while still putting some pressure on the string so it keeps ringing. Try and use all three fingers to bend the string, not just the third finger. Then, return the note to it's original pitch.

Chances are, when you first attempt this, you won't get the pitch to change much. This will be especially true if you try bending on an acoustic guitar - they are much harder to bend strings on. Be extremely patient... chances are you haven't used these muscles before, and they'll take time to strengthen. Keep practicing, and you'll get the hang of it eventually. Be sure and listen to the audio clip to hear what the bend should sound like.

A Harder Bending Technique 

This exercise is exactly the same as the one above, except this time, we're going to attempt to bend the note up two frets (a "tone", or a "full step"). Start by playing the tenth fret, then the 12th fret, to hear the pitch you're trying to bend the note to. Now, while fretting the note on the tenth fret of the second string with your third finger, pick the note, and try to bend it up to the 12th fret, then return it to it's original pitch. Remember: use all three fingers to help bend the note, or you'll never be able to push the note far enough.

Things to Remember:

• If the note is 'dying' before you've completed the bend, you've probably stopped exerting enough pressure against the fretboard to keep the note sounding. You HAVE to use all three fingers Make sure you're pushing the strings in the direction of the sky, not the ground. Bends are almost always done on the top three strings, as they are lighter, and are easier to bend. It's easier to bend strings on the higher frets on the guitar. Down near the headstock, it gets very hard to bend.
• It will take time to master this technique, so be patient.

http://guitar.about.com/library/weekly/aa031401e.htm