Apple will be releasing iOS 12 overnight tonight/tomorrow morning. It will come with a whole heap of exciting new features as well some key security and bug fixes.
As with all major software updates, it is always good to Back Up your device before upgrading to the new software. Although they shouldn't, things CAN go wrong. Fortunately Apple gives you 2 easy ways to achieve this:
iTunes
Plug your iOS device into your PC or Mac running the latest version of iTunes.
Click on the small thumbnail of your device next to the Music drop-down menu. In the Summary section, choose Back Up Now. You have the choice to either back up to iCloud or This Computer. In both cases, it is a good idea to select Encrypt iPhone backup/Encrypt iPad backup.
*Ensure you don't forget the password you choose, otherwise you won't be able to restore the device from the backup, should anything go wrong.
iCloud
You can also back up to iCloud directly on your iPhone or iPad.
On your iOS Device, go to Settings > tap on your name > iCloud > iCloud Backup > Back up now
Ensure your device is connected to both a WiFi network and charger. This process can use up a lot of data and battery power.
Whilst this method is the easiest and most convenient way to backup your device, there are some things that are not included in this method:
Data that's already stored in iCloud, like Contacts, Calendars, Notes, My Photo Stream, iCloud Photo Library, iMessages, and text (SMS) and multimedia (MMS) messages
Data stored in other cloud services, such as Gmail and Exchange mail
Apple Pay information and settings
Touch ID settings
Therefore we recommend the iTunes method of backup to ensure you have everything you need.
More information on iOS 12 can be found directly on the Apple Website