1. Use parameterized queries or prepared statements when working with databases to prevent SQL injection attacks. Avoid concatenating user input directly into SQL queries.

2. Validate and sanitize user input before processing it to prevent cross-site scripting (XSS) attacks. Use functions like htmlspecialchars() to convert special characters to their HTML entities.

3. Use strong, unique passwords for all accounts and encourage users to do the same. Implement password strength requirements such as minimum length and a mix of alphanumeric and special characters.

4. Always escape output when displaying user-generated content to prevent XSS attacks. Use functions like htmlentities() to convert special characters to their HTML entities.

5. Set secure session settings, such as using HTTPS to encrypt communication between the server and client and using secure cookies to prevent session hijacking.

6. Implement proper access control measures to ensure that users have appropriate permissions for the actions they are trying to perform. Use role-based access control (RBAC) to assign roles to users and define their access privileges.

7. Enable two-factor authentication (2FA) for user accounts to provide an extra layer of security beyond passwords.

8. Keep your PHP version up to date to ensure you have the latest security patches and bug fixes. Regularly update all dependencies and libraries used in your application.

9. Secure file uploads by validating file types, checking file size limits, and storing uploaded files outside of the web root directory.

10. Regularly monitor and log any suspicious activities on your server. Implement a system for monitoring and responding to security incidents.