Don't Install It If You Haven't Prepared
Apple's iOS 9.1 update is the first milestone upgrade for iOS 9. It's a much larger update than iOS 9.0.1 and iOS 9.0.2. Big iOS updates can have a big impact on your devices performancae so you'll want to be extremely careful with iOS 9.1.
If you haven't done any prep work ahead of your iOS 9.1 install, you're going to want to hold off until you're able to clear some time to prepare yourself, and your device, for this software change. This is extremely important if you're coming from iOS 8 or something older. iOS 9.1 is a big jump.
We've recently put together a list of steps to take before installing the iOS 9.1 update on your device. Some of you might be able to get this done in a few hours. Some of you might need a few days. Take your time, prepare for iOS 9.1, and then install it when you're ready.