Use Your "Rolling" FastPass
Before arriving, you can book up to three FastPasses for rides in the same park online (30 days before, unless you're staying at a WDW resort, then it's 60 days!), then once you have used them all, you can use the My Disney Experience app to make an additional FastPass reservation. Once you use that one, head back to the app and repeat! Pro tip: schedule your reservations for as early in the day as possible, so that you have time to book more throughout the day.