Restart your iPhone
Update iOS to the latest version
Delete large message attachments
Clear Safari history and website data
Remove downloaded offline content from apps
Delete unused apps
Offload apps you do not use
Clear app caches inside app settings
Delete and reinstall apps with large caches
Remove old iOS update files
Delete downloaded podcasts, music, and videos
Reduce photo and video storage by using iCloud Photos or transferring files
Delete duplicate or unnecessary photos and videos
Clear Mail attachments and old emails
Remove old iMessage conversations with large attachments
Reset network settings
Back up and restore your iPhone
Factory reset and set up as new if needed