***Videos take up the most space, this is an easy way to free up storage right away. After deleting photos/videos, make sure to go to your photos, then albums, and to the "recently deleted" to delete them permanently - if you don't do this, your device will still save these items as a safety precaution in case you change your mind.
Select "Manage Storage" under Storage
You should now be able to see your Used & Available storage space on your device. You can also see the applications and how much space each one is using. (You can use this information to decide whether you really want to keep something, or to help decide how much to get rid of.)
*Make sure you check out the next page Storage - iCloud to make sure that has enough space to backup.