Apple provides you with only 5 GB of free iCloud storage, which is hard to use effectively in an era of 256 GB phones. Therefore, a fast guide to maximize your storage is provided here.
1. Manage what you back up
iCloud lets you choose which apps you can include in your back up. Not every thing on your phone is irreplaceable or worth back up. See what takes up the most space, that you can simply download again.
2. Don't use iCloud photos
This setting automatically backs up your full resolution photos to iCloud, and reduces space on your physical device. If you're running out of space on both, you can backup photos to your computer and delete the high resolution originals.
3. Give up and buy more storage
Clearly, giving you 5GB in an age of phones with massive storage space is a ploy to get you to buy more storage. However, at just 99c for 50GB, it's a pretty cheap ploy that is probably worth biting the bullet for.