Sometimes a good idea to ask how much experience everyone has as well.
Had a useless observer at Brands a couple of seasons ago whose briefing consisted of, "Right, you all look like you know what you're doing, I'll leave you to sort yourselves out, have a good day", and with that went back to his hut to get a coffee.
Don't know how he came to his assumption as nobody on the post had been marshalling for more than 2 seasons and two were still novices. Questions were met with "I'll let you decide" or "That's up to you". We were fuming, but as it was, when things did happen we coped, and given his general level of incompetence, we were quite glad he stayed out of it!
So I'd say don't assume people know what they're doing - better to teach grannie to suck eggs than see grannie mown down by a Formula Ford!
Phill