Just to throw my two cents in,
The standby is a major rule, and make sure you establish it early. There's nothing worse than trying to call complicated sequences when people are yattering.
I always refer to sections of script where idle chatter is allowed as downtime, so I'll actually announce "thanks everyone, good sequence, we're in downtime again", and then they know it's alright to talk.
Call ons and offheadsets, not the immediate second you put it on though, try and listen in case we're in a standby or a calling sequence.
Establish a standby order, and make people hold to it. Mine is generally LX, Sound, Video, Mics, Flies, Trucks, Traps, Actor cues. So make sure people hold to it, it makes it much easier to isolate out if a particular element is missing.
Don't chew gum, eat or drink into a headset.
Train your crew to acknowledge a headset check, followed by a volume check, and once that's checked and everyone is properly audible they will ideally not have to fiddle with their headsets.
Don't let anyone say anything that they'd be ashamed to say out loud, it's a pretty good general rule, because ultimately you're one of the ones responsible for what is allowed to be said on headset, if your tech team starts badmouthing actors, directors or anyone else and someone hears, someone's going to point the finger at the SM for why didn't they stop it.
Don't ever drop a headset or let it clatter, mic on or off. We have wireless packs that are becoming damaged because people don't secure them to their belts properly, their range has dropped by almost a third from when we first got them.
Hope that helps.