There is no single approach Dan. If I am at a site that hasn't been totally cleaned out of high conductors (are there any such sites left ?), then I would start with 8 or 12 kHz, Reactivity 1 or 2, Silencer = 0, Disc = 8. Once the "easy" targets have been cleaned out, I like to hit it with 18 or 28 kHz, still using R=1 or 2, S=0 or 1. The plan of attack for detecting in iron is quite different. Typically use higher frequencies and higher Reactivity, some Silencer.
A lot of settings just boil down to personal preference. I like Multi Tones because full tones annoy me. Discrimination I usually have at at "0" or "8". Just depends on how much noise I feel like hearing.