What sorts of files can I remove from my iphone 10 to reduce icloud use. And how do that? So far, all I get from Apple iCloud are solicitations urging me to buy more storage space on iphone...rather than how to reduce what I ihave!

iCloud says I'm running out of space. in the cloud. I only use it for my iphone 10. What do I need to remove to keep my space use under control on the phone? Remove unused apps? messages, etc. I do not keep email on my phone. Apple seems determined to just solicit me for more storage space! Seems wasteful to me... especially since I'll have to pay for it. I can find no supporting information about how to keep icloud storage to a minimum. If I offload all my photos to a an external drive, will that do it? What's the easiest way to do that? Thanks