As far as how to mount the mics, see this site...Jason's a sound guy out in Vegas who definitely knows what he's talking about (in fact, I was going to do a similar web
page, but decided not to when I found Jason's, because his covers everything I was going to, with pictures and everything!):
http://www.brightandloud.com/microphone-placement/.
As for mixing, Mike's advice above is pretty spot-on, with one minor quibble. Mike says line-by-line mixing involves ducking the non-active onstage mics by 10 dB or so. In some situations, yes, I'll resort to that, but whenever possible, you should pull them all the way out (of course, we're referring to onstage actors here...all offstage actors are down all the way as a given).
It's a lot of finger gymnastics, and takes some practice as well as knowing the script COLD, but it's the best way to get a good sounding mix. Start out as Mike suggested just pulling back partway, since there's a little more room for error that way (if you miss a pickup, the mic will at least be up, if not as loud as it ought to be). But, as you practice and get better, the end goal should be to pull the mic all the way down unless absolutely impossible--for example if there's a trio going on and you need to rapidly
bounce between three mics, you can get the coordination down to
duck the two that aren't currently active, but if things are going fast enough, you just won't be able to constantly pull the mics down.
The hardest thing, as Mike hinted at, is mixing duets. One of the last off-Broadways I mixed only had three actors, so you'd think it'd be a simple show, but it was the most challenging show I've ever mixed in that it was all about duets. Every scene had a major duet, and in many of them the lead couple would be dancing up close while singing together, and then the woman would spin out (while still singing), then spin back in and immediately shout, "Noooooo, Gino!" right into the man's mic, then spin back out again...you get the idea. It just became a matter of fingers flying really fast, and learning which mic would
pick up the opposite actor at which distance, so that I could make the transition from one mic to two back to one and have it sound clean.
Again, though, while you avoid some of these problems with mixing floor and hanging mics, for a
play, it's not all that different to how you should be mixing those fixed mics. Even with those, you want to avoid having more than one up whenever possible, it's just that there you're following the
blocking first, and then the script, whereas with wireless you're primarily following the script, and then the
blocking for things like duets.
--A