Most aviation authorities will have a list of things they want you to include in a brief. The UK CAA certainly does in our ANO. I wouldn't regard that list as comprehensive, but you probably should include what the regs say you should.
I echo Arismount's views that if you really want a pax to remember something, get him to do it himself. People lose any brains they ever had around helicopters, and memory of a task performed is better than one discussed or shown.
An example would be to get them to latch and unlatch the seatbelt/harness. It is surprising how many "experienced" passengers are not aware that you need to operate an seat belt latch in an aircraft further than a car to get it to open. The same applies to the door lock/latch mechanism.
It also probably makes sense to tell the pax what is planned. For example, if you can, it is probably best to get the pax in before start and shutdown before letting them out. It is sensible to explain what you plan (even if the plan may change).