Right,
Bending is one of 'those' techniques. It takes years to learn how to do 'properly' and you can do it for years without realizing your doing it wrong.
As far as what notes to bend, you need to keep in mind the 'destination note.' That is, the note that you are trying to achieve by doing the bend in the first place.
Take position one of the minor pentatonic in A - you have:
e--------------------------------5--8--
b--------------------------5--8--------
g--------------------5--7--------------
d--------------5--7--------------------
a--------5--8--------------------------
E--5--8--------------------------------
Theory-wise, this is A-C-D-F-G over 2 octaves. So, you can basically take any note on the fret board and bend it to one of these 5 notes. But it's not just these 5 notes you can bend to, there's one more that isn't in the minor pentatonics, but is probably one of the most used bends - that would be the V of A which is E.
Take the 7th fret of the G string, and bend that up two semi-tones for E.
From there, another way to know which notes you can bend in the first position is to learn the second position of the the minor pentatonics:
e------------------------------------8--10--
b-----------------------------8--10---------
g-----------------------7--9----------------
d----------------7--10----------------------
a---------7--10-----------------------------
E--8--10------------------------------------
By knowing this position, you know which notes you can bend and by how much, i.e. if you wanted to bend the 8th fret of the high e, you know you can bend it a tone. But, if you wanted, for example's sake, to bend the 7th fret of the d string, you'd have to bend it a tone and a half.
It's a really good idea to learn all 5 positions of the pentatonic scale, major and minor. Don't fret, though, because they are one and the same! They just start in different places. Position 1 of the major pentatonic is the same scale as position 2 of the minor pentatonic - that's what Robert was talking about a few threads ago.
Now onto the actual technique of bending.
*Note* - This will be **very** difficult on a steel string acoustic considering the thickness of the strings. Be very careful, if you start to feel *any* pain what so ever then STOP. A burn is normal, a pain is not.
Now, let's start with an anatomy lesson as to why it's so important to bend string properly. In your hand there literally dozens of tendons, but no muscles. The muscles controlling your fingers are in your wrist and forearm. The tendons in your fingers are very small, the longest will be substantially less than an inch. The strings of a guitar are tuned quite tightly, to around 30lbs or so of pressure on the high E, let alone the low E. These tiny tendons can not take this kind of weight. But what can? How can you distribute this weight evenly and effectively? Through your wrist, that's how.
What you are meant to do is have your hand at an angle to the neck, i.e. (keep in mind I have small hands) if I wanted to bend the 7th fret of the G string with my ring finger, the first knuckle of my index finger is practically touching the 4th fret. Angle. Another thing, there is *no gap* between the webbing of skin that stretches between the index finger and thumb and the neck of the guitar. If there is, it will be less than a centimetre.
Now - the important bit - you *pivot* your hand on your wrist where the webbing of skin touches the neck. Your fingers remain *straight* the entire time. They should not bend, because if they do, it means those tiny tendons are taking the weight instead of the nice chunky muscles and tendons in your wrist and arm.
I will leave it at that for now, I hope it helps!
Just give us a shout if you have any further questions!
And remember: have fun!
