Introduction to Zone Focusing

Eric Kim gives an excellent explanation on "Zone Focusing" for streetphographers and how to setup your camera so it is always ready. 

From his blog:
"For those of you who aren’t familiar with zone focusing you essentially use a high f-stop number with a deep depth of field (f/16 or f/11) and have your camera pre-focused to a certain distance to get your photos in-focus. This is beneficial because although modern autofocusing systems are quite good, they are not 100% reliable. Using zone focusing when shooting street photography allows you to get far more keepers."

Read further.