thumb placement:

for bends let the thumb hang slightly over the neck

support from other fingers:

When bending with the 3rd finger, place the 2nd finger in the fret directly behind it and push with both fingers

muting unwanted strings:

when bending up with the 3rd finger, allow the 1st finger to cover some of the lower strings to prevent them from ringing.

Push or Pull?

Depending on the situation, you will either push up on a string, or pull down. Generally you will push up to bend on the 1st 3 strings ( it is possible to pull down on the 3rd). For the 4th, 5th, and 6th strings, it is most common to bend by pulling the string downward.

How far should I bend?

When your bending a string you should be aware of the specific pitch you are bending to. In most cases it will the note 1 fret higher (half step bend), or 2 frets higher (full bend). it is possible however to bend 1/1/2 and even 2 steps.

Practice hearing how far you bend. One way to work on this is to 1st hit the note you are trying to bend to, then bend the string until you hear it reach that pitch. For example try bending the 1st string at the 8th fret a full step, but 1st hit the string at the 10th fret to give your ear a point of reference.