Pillion passengers are a safety issue on motorcycles. Poor briefing can endanger the passenger, driver and bike. Here's the UK-based Motorcycle News on pillion riding.
Some motorcycle dealers will provide a pillion passenger orientation session.
Some advanced training courses allow pillion passengers to participate. Check with the training vendor. We are unable to find any specific pillion training in the US. Please check the link above and instruct your passenger accordingly.
The rider/driver should have some experience on the motorcycle before taking a passenger, like a year or 5K miles. The passenger should be briefed on procedures beforehand.
The motorcycle will handle differently with a passenger, including longer braking distances and different center of gravity. You will need to adjust the suspension preload (see the Motorcycle News article for more).
The passenger may need to be cautioned against hot parts, including pipes and brake rotors.
There is a disturbing trend in rural motorcycle accidents, where the bike goes off the road, for the paramedics to find the rider, but not the pillion passenger. Read our blog posting on the subject.
Of course, the passenger needs full protective gear, just like the driver.