Check iCloud storage usage: Settings > [your name] > iCloud > Manage Storage
Review and delete large items in iCloud Drive: iCloud Drive > select files/folders > Delete
Remove unwanted photos: Photos > select items > Delete (and confirm removal from iCloud)
Disable iCloud Photos temporarily (if needed): Settings > [your name] > iCloud > Photos > turn off Sync this iPhone
Delete iCloud email attachments: Mail > open messages with large attachments > delete attachments or messages
Clear iCloud backups: Settings > [your name] > iCloud > Manage Storage > Backups > select device > Delete Backup
Turn off app data syncing for apps you don’t need: Settings > [your name] > iCloud > turn off apps under Apps Using iCloud
Reduce iCloud syncing for specific apps: Settings > [your name] > iCloud > Manage Storage > select app > delete data if available
Delete old shared items: iCloud > Shared with You / Share settings > remove items you no longer need
Manage iCloud Drive shared folders: iCloud Drive > shared folder > remove yourself or delete shared content
Empty Recently Deleted for Photos: Photos > Albums > Recently Deleted > Delete All
Empty Recently Deleted for Files (if applicable): iCloud Drive > Recently Deleted > Delete All
Sign out and back in only if needed: Settings > [your name] > Sign Out (then sign back in)
Upgrade or change storage plan if you need more space: Settings > [your name] > iCloud > Manage Storage > Change Storage Plan