Use the Door Rail as a Guide
The location of knobs and pulls isn't written in stone, but there are some standard practices. One good rule of thumb is to line up a knob with the top of the bottom door rail. If you're installing door pulls, line up the bottom of the pull with the top of the door rail. Always center them on the door stile.
Temporarily Attach the Hardware
If you're not sure about where the knobs and pulls are to be installed, stick a piece of reusable putty adhesive to the hardware and try out different spots. Mark the one you like with a pencil and install the rest of the hardware accordingly. Reusable adhesive is available at hardware and art supply stores.