It depends on what type of tap is being used. First of all you need a counterbore or pre-drill for the unthreaded part of that particular screw. This requires a separate feature created before the threaded hole so the cosmetic thread has a good start surface.
This is a pretty nice guide for the pilot drill depth courtesy of:
http://tapmatic.com/images/pdf/Drill%20Depth%20Clearance.pdf
