When you take the passenger's seat on a motorcycle, it is not like sitting in a car. You actively affect the handling of the vehicle, and hence the rider's ability to control it. So, it's important to know how to be a good passenger. It's not difficult, but many people don't get it.

When riding in a straight line, it's pretty much a no-brainer; just don't make any horrible lurching sudden moves and everything's peachy.

Things get a bit more complicated around corners. I've found that most people tend to try to remain upright as the bike (and rider) lean into a corner. This is a Bad Thing; it profoundly changes the handling characteristics of the bike. Here's what you should do: As you approach the corner, look through to the exit of the curve, making sure you only tilt your head to stay parallel with the ground, rather than your whole body. Your torso should not move in relation to the rider's torso. I guarantee that your rider will thank you. And even if he or she doesn't, you'll definitely be safer for following this simple rule.

So far, the best passengers have been girls (like Wintersweet and Yumi), but there is no convincing experimental evidence that suggests a sex/passenger competency correlation, as the statistical sample is yet far too small.