SAFETY is yet another of the myriad of mnemonics sometimes used in general aviation. I use SAFETY for briefing passengers when I'm flying in small planes. Although the potential informality of small aircraft is almost intoxicating when compared to the procedures and regulations of commercial flight, safety (hence the name!) is paramount, so it's always a good idea to make sure your pax know what to expect and how to behave. I generally go through this prior to engine start-up, when it's safest for me to be paying attention to the passenger.
Seatbelts - show them how to fasten, adjust and release the seatbelt (or have them demonstrate). I advise all my pax to leave their belts fastened at all times.
Air - show them how the cabin vents work. If it's cold out, explain that cabin heat will be available when the engine warms up, adjust as necessary, and ask them to either ask me to adjust it or make sure I'm watching, because the control on the Cessnas I usually fly is behind the right-hand control yoke.
Fire precautions - if available, show them where the fire extinguisher is. Instruct them not to use it unless I clearly tell them to, and reassure them that fire is incredibly unlikely.
Exit - show them how the door controls work (open, close, lock) and make sure they know that whenever exiting the airplane they should walk towards the rear because the prop is dangerous as all heck.
Traffic and Talk - encourage them to report anything they see in the air to me to make sure I know about it - birds, airplanes, superman, whatever. Also at this point I tend to go over the 'sterile cockpit' concept, and request they not talk to me until we have taken off and I have stated that I'm available to talk - so I don't get distracted from checklists or communications or of course flying the airplane. Later, when the engine is running, we'll set headset and intercom volumes as appropriate.
Your questions? - encourage questions!
Once I begin the startup checklist, other than asking them questions as part of that process, sterile cockpit should apply until climb-out at the earliest, or possibly until cruise.
In addition to the above, I like to tell new fliers what to expect. Something along the lines of "We're going to taxi to just short of the runway, and I'm going to stop to do a final check which will involve running up the engine. Once we're ready to go, I'll check with you to make sure you're ready, then I'll make a radio call. We'll taxi onto the runway and depart. It may seem like we're climbing at a high angle compared to a jetliner, but don't worry, that's normal. Now, in case something goes wrong during the roll, I'm going to abort the takeoff - just yank the power and brake us to a stop, we have more than enough runway. If something goes wrong immediately after takeoff, I will be determining whether to try to land on the runway, or whether I'll need to land straight ahead somewhere. If you try to talk to me and I'm busy, I'll hold up a finger to let you know - usually it means I'm listening to someone on the radio. Okay? Great, let's go flying!"