How to properly use input validation and sanitization to prevent security vulnerabilities?

Proper input validation and sanitization are key to securing your application. Always validate input against a defined schema, and check for the following fields:

• Data type,
• Format,
• Length,
• and Range.

Also, use existing libraries or frameworks for validation to avoid reinventing the wheel. You should sanitize data by removing or encoding potentially harmful characters, especially for inputs used in SQL queries, HTML content, or URLs. Finally, apply validation both on the client and server sides, but never rely solely on client-side validation for security.