When I brief passengers I cover the following topics (and generally in this order):
1) Operation of the doors (tell them and show them)
2) Operation of the seat belts (ditto)
3) Operation of the headsets (voice-activated or not)
4) Operation of the lifevest (when appropriate)
5) Embarkation/disembarkation procedures (e.g. will someone escort pax to/from the acft; will I escort them; shut down or no shut down etc.)
6) A warning about the dangers of both the tail rotor and the main rotor
If you don't have the ability to isolate your own audio you may want to add something about being quiet during certain phases of flight.
Have a nice flight and thank you for flying (insert your name here) airways...
Forgot to share this true story with you. Here goes:
A friend of mine told me about a one time colleague of his who learned to do a good pre-flight briefing the hard way. He once loaded some passengers into a B206, two in the back and one up front, without telling them anything and without removing the dual controls either. When they get to their destination the pilot keeps the helicopter running and instructs the passengers to disembark. The passenger up front has no idea how to open the door and, in the absence of clear instructions from the pilot, simply pulls up forcefully on the handle to the left side. You guessed it, the collective!
So don't forget to tell them about those doors and don't forget to remove the duals!