Apple sold 10 million iPhones on launch weekend, while millions more users installed iOS 8. As I did last year, I've been working to identify solutions to some reported iOS 8 problems, so if you're having problems take a look at these suggestions first.
Don't panic!
Apple's engineers are already actively finding solutions to snags that have emerged now the OS is available and will resolve many in the next software patch.
As an example, a Reddit post talks about Apple engineers working with one iOS 8 user to identify and resolve a problem with Family Sharing and older iTunes content.
Be sure to follow these instructions when upgrading.
Space invasion
iOS 8 demands around 5GB of available space for installation if you upgrade wirelessly, but less if you use iTunes to upgrade. Instructions for using iTunes are included in this previous report.
Dropbox and Microsoft One Drive offer good quantities of space to save your images and videos -- or you can export images to a Mac or PC before deleting them.
Warning: Do not upgrade to iCloud Drive unless you are already running OS X Yosemite, as you will be unable to access documents stored there using the current version of OS X.
All the 'R's'
Slow performance? Apps crashing? Then you should try these three basic steps first: Restart, Reset or Restore, as between them they usually resolve most problems. Always backup your device first.
Restart: Switch off your device by depressing the power button until the "slide to power off" bar appears, then swipe. Once the device is off, hold down the power switch to restart.
Hard Reset: Press and hold both the power and Home button until the device restarts with an Apple logo. This has proven effective when dealing with network connectivity problems.
Reset: If the problem recurs, the go to Settings>General>Reset. Choose Reset All Settings. This keeps your media and other files intact, though you'll need to re-enter your settings. This seems to improve performance.
Restore: The most time-consuming patch and you must have a recent backup before you begin. Connect your device to iTunes and choose the Restore option in the top pane within Summary view. The device will be returned to factory condition. Restore is often the most effective troubleshooting step.
Selected specific hints follow: