Before selling your iPhone, there are several things you should do to ensure that your personal information is removed and your device is ready for its new owner. Here are the steps you should follow:

1. Back up your data: Create a backup of your data using iCloud or your desktop computer using iTunes.
2. Unpair your iPhone from other devices: If you paired an Apple Watch with your iPhone, unpair your Apple Watch.
3. Cancel your AppleCare plan: If you purchased an AppleCare plan for your device, cancel your AppleCare plan.
4. Log out of apps and remove personal information: Sign out of iCloud and the iTunes & App Store, and remove your personal information from your device.
5. Erase all content and settings: Go to Settings > General > Transfer or Reset iPhone > Erase All Content and Settings.
6. Remove the SIM card: Take out the SIM card.
7. Clean your device: Use a soft dry cloth to wipe the front and back of the device. Carefully clean the speaker grills, earpiece, and other such places too.
8. Remove your phone from your Apple account: Remove your phone from your Apple account.
9. Deregister iMessage: If youre switching to a non-Apple phone, deregister iMessage.
10. Contact your carrier: Contact your carrier for help transferring service to a new owner.

By following these steps, you can ensure that your personal information is removed from your device and that it is ready for its new owner.