always mount before the passenger, and tell them when you are ready for them. The passenger should get off first, again only after you tell them you are ready. Tell them to keep their palms on the tank (if its a sportbike) especially when stopping. When stopping, squeeze the tank with your legs so the passenger doesnt crush your giggleberries.
The lighter the chick's weight, the easier the ride/learning process will be. Dont haul thick chicks until you know what you are doing.
GEAR. Get passenger gear. Gloves, helmet, boots are essential, leather coat preferred. Do not let your girl ride with sandals and no gloves. Imagine how shitty you would feel if you fucked up those pretty fingers or toes.
Remember, if the passenger has never ridden before, it takes very little for them to have fun. You dont have to stretch the bike to its limits trying to impress them, just cruise.