What is the best way to handle a dog who snaps at you?

Correcting doesn't seem to do anything but make him angrier...he's a 5 lb Chihuahua (realize they are somewhat snappy to begin with) who had been mistreated...not exactly sure how much he was mistreated so I don't quite know how to handle his temperament. He seems to get snappy when he is tired. Can't do much to change his mind either.