It's iOS upgrade time again, and this is your regular reminder to perform a backup before upgrading. You shouldn't have the disc space issues that last year's upgrade experienced but there is an additional step to preparing if you want to keep all your data safe.
This time around, if you want to keep your Health app data (which might be of particular interest to you Apple Watch owners) then you need to do an encrypted local backup. Connect your phone to your computer and fire up iTunes. On your iPhone's summary page, in the backup section, check the box for Encrypt iPhone Backup, follow any prompts that this triggers and then hit the backup button. This will save away all your health data in case you experience an issue with the upgrade. Should you need to restore your phone do so via iTunes selecting this backup and you shouldn't lose anything.