Briefing
I see you are located in the U.S. So, start by complying with FAR 91.107. Then, although the section is not regulatory for your helicopter, you might read FAR 91.519 and see what items are covered there. Finally, the best solution, as someone has mentioned, is to contact Robinson and obtain a passenger briefing card which you could use as a guide to brief your passengers and then let them look it over again before the takeoff and before the landing. What Confucius said many centuries ago definitely applies to passenger briefings: "I hear, and forget; I see, and remember; I do, and I understand."