A favorite trick of cabinet designers and fabricators is to mount the knob slightly above the center line (vertical) on the drawer. This helps make the knob look like it is centered when the cabinets are viewed from above (as if you were standing at the countertop looking down). The amount of offset is up to the installer, but starting with 1/16" and up is a good place to start.
For hinged doors, it is important to avoid placing the knob in the corner of the door frame. Placing knobs in the corner can weaken the cabinet's joint. We recommend placing the knob in the upper third, but with many traditional-style cabinets a knob in the center of the door stile (vertical) can be pleasing. Both options provide more leverage.