Delete old backups: Settings > [your name] > iCloud > Manage Account Storage > Backups
Turn off backup for apps you do not need: Settings > [your name] > iCloud > Manage Account Storage > Backups > [your device]
Delete large photos and videos from iCloud Photos
Empty the Recently Deleted album in Photos
Turn on Optimize iPhone Storage: Settings > Photos > Optimize iPhone Storage
Delete unnecessary files from iCloud Drive in the Files app
Remove large attachments from Messages: Settings > [your name] > iCloud > Manage Account Storage > Messages
Delete old messages and conversations with large media
Clear Mail attachments by deleting large emails from iCloud Mail
Review and delete app data stored in iCloud: Settings > [your name] > iCloud > Manage Account Storage
Remove unused device backups from old iPhones or iPads
Turn off iCloud syncing for apps you do not use: Settings > [your name] > iCloud
Delete voice memos, notes, and other synced content you no longer need
Check shared albums and remove unneeded items
Upgrade to a larger iCloud storage plan if needed