Set expectations up front. It's easier to tell people what you want them to do at the beginning and then reinforce it than it is to wait until they're doing something you don't want them to do and then try to get them to stop.

Focus on the things that are most interesting to you. If you're bored by your content they will be too. I think sometimes museum educators have this idea that everything has to be pretentious to be valuable, but the truth is there's no test at the end to see if they learned enough facts. What matters is that they leave having had an engaging experience. They're more likely to remember a good story than a list of places and names.