for a slow vibrato you can apply harder and lighter pressure on the string. for a fast, bb king-like vibrato, use your finger tip as a pivot point an kind of just wiggle your hand. its hard to explain, but youll get it. you an use combinations of the 2 to find just what youre looking for
You do not merely want to be considered the best of the best. You want to be considered the only ones that do what you do. - Jerry Garcia