You get them going on a nice straight track and they think 'This looks smooth,' and then you dip it down a little to give them a good jolt. Or you have it so that when they go over a hill it looks like they're going to get their heads chopped off at the bottom."
To get them moving along a consistent, even course, you start by making it seem effortless, and then you introduce a slight dip to create a sense of surprise. Alternatively, you plan the route so that when they reach the top of a hill, it seems like their journey will culminate in a dramatic conclusion at the bottom.