Depending on where you take the test you may ride on a 30cm plank rather than between two lines. In either case, you will want to follow these steps:
Don't ignore the advice in step #2. If you look down and carefully try to stay on the path, you will probably end up watching yourself go out of the lines. If you can ride steadily, then you should be fine if you just aim toward the end of the path and go.
If you can't stay in the lines, you will want to work on stabilizing your riding. Work on the basics: Back straight, lean slightly forward, keep your weight on the seat.