when you bob and weave, you dont bend from the knees, you bend from the waist.
My trainer is teaching me the bobbing and weaving style.

when your in the straight punching range, its best to use the side to side head movement. but when he gets closer, then u start bobbing in a "U" kind of movement.

If your also a bob n weave kind of fighter then you should always try staying in close to your opponent, parry his shots and quickly close the gap and work the body/head....etc