1. Back Up Data: Ensure all significant data is backed up to a secure location, like an external hard drive or cloud storage.

2. Encryption: Encrypt your device using device encryption features, such as FileVault on Mac or BitLocker on Windows, to scramble your personal data.

3. Sign-Outs: Log out of all your accounts, including email, social media, and online banking.

4. Reset to Factory Setting: Perform a factory reset on the device to erase all your data and applications.

5. Remove Additional Information: Remove SIM and memory cards if applicable, to ensure personal data is not accessed through these.

For Android:

1. Google Account: Remove your Google account from the device to eliminate access to your personal information and services.

2. Samsung Device: If selling a Samsung device, visit Samsung's "Find my Mobile" website and deregister your device.

For Apple Devices:

1. iCloud and Apple ID: Sign out of iCloud and unlink your Apple ID from the device to prevent access to personal data.

2. Deactivate "Find my" Features: Turn off "Find my iPhone," "Find my iPad," or "Find my Mac" to remove devices from your account.

3. Erase All Content: Perform an "Erase All Content and Settings" to thoroughly erase all data from your Apple device.

4. Unpair Apple Watch: If selling an Apple Watch, unpair it from your iPhone to remove any personal information.

Additional Steps:

1. Review Terms and Conditions: Thoroughly read the terms and conditions before accepting when resetting or deleting personal data.

2. Physical Destruction: If you have old or outdated devices with data you can't erase due to damage or other factors, consider physically destroying the device to prevent data recovery attempts.

Remember, even after taking these steps, it is still possible for data recovery experts to retrieve information. If there is highly sensitive data, consider professional data destruction services to ensure complete erasure.