Ready to trade in your old iPhone for the newest one? Before you do, take a look at this checklist to make sure you've deleted all important data from your iPhone. Don't leave anything behind!
An important tip! Whatever you do, don't manually delete contacts, photo streams, calendars, or reminders while logged in to your iCloud account. This will also delete the content from the iCloud servers and your iCloud-connected devices (like your iPad or laptop).
Another important tip! If your phone accidentally runs out of battery during the "restore to factory settings" step, use iTunes to erase data. Connect the device to your computer, then restore the backup. Connect your phone to power, go to Settings app > General > Reset > Erase All Content and Settings again.
OK, but seriously, this is the last important tip! You can erase your device remotely. If you set up Find My iPhone, sign into icloud.com/#find, then click on All Devices and select the phone you want to erase. In the info window, click "Erase iPhone." You'll need to enter your Apple ID password.