I know it's hard to resist the temptation to start smashing that "Check for Upgrade" button in iOS as soon as Apple releases an update, but carrying out a few simple checks in advance of downloading the upgrade can make all the difference.
1: Check that you're actually going to get an upgrade. Only the following devices are supported, so if you have something older, it's time for a new iPhone or iPad:
2: Back up your data. Don't take chances with those precious photos or important notes! Details on how to carry out a backup can be found here (if you want to back up your Health data, you will need to carry out an encrypted backup).
3: While it's likely that your device automatically updates apps in the background, it's not a bad idea to check just to make sure. Find the App Store app, tap on it, and click on Update (bottom-right of the screen). Once in there, you can kick off the update process.
4: You're going to need some of your passwords (such as your iCloud password), so make sure you know them in advance, or you might end up in a world of hurt.
5: Plug in -- it's better to carry out the upgrade while plugged in, just in case you run out of juice!
6: Over the air (OTA) is the quickest and least-hassle way to download a new iOS update (Settings > General > Software Update), especially if you have good Wi-Fi and a speedy internet connection. However, if that fails, you may need to hook up to your PC or Mac that runs iTunes and carry out the upgrade from there.
7: Consider holding out for a few days, if you rely on your device, just in case there are any show-stopping bugs. It's likely that there will be a couple of iOS 10 updates over the coming weeks.