Backup Your Data
This is extremely important.
Before you download the iOS 11.4 beta on your smartphone or tablet, make sure you make a backup. There's always a chance something could go awry so you'll want to make sure all of your important data (photos, music, etc) is secure before making your move to the beta.
If you don't know what this means or simply don't know where to start, we've put together a guide that will take you through the backup process via iTunes.
If you don't want to make a backup through iTunes, you can also use the backup process provided by Apple's iCloud service.
Make sure you do this before proceeding. Otherwise you could wind up in one of the horror stories we hear about each and every time Apple releases a new beta.