The general rule is that the closer the mic is to the subject's mouth, the better. If we could implant mikes inside people's mouths, that would be ideal. Barring that, keep the mike as close as possible. Of course, this is limited by the need to stay unobtrusive. So stick mikes should be 6-12 inches away (as in the photo at the right); lav mikes at the first or second button; and boom/fishpoles just off-camera.