Have all of your components laid out ahead of time.

I place stuff that doesn't normally need to be touched or viewed (amps, sat boxes, etc.) on the bottom.

DVDs and CDs should go at a comfortable height for loading and looking down into the trays.

PrePros/Receivers should go at eye level.

Plan your power distribution very carefully. Make sure that you have enough jacks for your plugs, and that your power cords will be long enough to reach your power strips.

I bundle signal cable and speaker wires on one side and power cables on the other side.

Use racks that are large enough to accommodate future expansion and will allow for proper venting panels.

That's just a few that jump to mind.