The placing of knobs is crucial to the overall integration of your cabinetwork. When placed with care a knob should blend into its context. Poorly placed knobs act as visual stumbling blocks to the balance of otherwise well proportioned cabinetwork. If most cabinetwork was on the cutting edge of modern design I would make no attempt to lecture on knob placing but the truth is that the vast bulk of new cabinetwork is very traditional in design and seek to evoke times past. The cult of "convenience at all costs" can lead designers and homeowners to sacrifice all the time and effort they have expended on solid hardwoods, raised panels and custom finishes and scatter knobs in the most non-traditional places. Here are a few thoughts that might help.
Never place a knob in the corner of a door, imagine the door length divided into four quarters and try to keep the knob in the middle two quarters. It does nobody any harm to stretch up or down a little.
Avoid placing knobs on raised panels. This cannot always be avoided, particularly when the cabinetmaker has seen fit to produce raised panel drawer fronts.
A knob should always be positioned a little above center on a drawer front, a centered knob will appear below center seen from above.
If a drawer is wide enough to need two knobs as a rule of thumb they should be set about 1/6th of the drawer length from each end. Take this as a starting point not a strict rule.