Your acceptance rate is the number of ride requests you've accepted divided by the total number of ride requests you've received while online. When a rider cancels a trip this does not count against your acceptance rate.
It's important to maintain a high acceptance rate to provide a reliable service for riders. However, if you'd like to take a break after your current trip, you can go into the trip menu and tap the status switch. Once tapped, it will change your status to "Offline" after you complete your current trip and turn black. Tap your switch bar again to go back online. You'll know you're online when the bar is blue.
If you're using an iPhone on iOS 9 or 10 and having trouble accepting trip requests while outside the driver app, visit the link below to change your phone's notification settings. This will make accepting trips easier.