Securing a web application against common threats like SQL injection and cross-site scripting (XSS) involves implementing several best practices:

SQL Injection:

1. Use Prepared Statements: Always use prepared statements and parameterized queries to separate SQL logic from user input.
2. Stored Procedures: Use stored procedures to execute queries.
3. Input Validation: Validate and sanitize user inputs by allowing only expected data types and formats.
4. ORMs: Utilize Object-Relational Mappers (ORMs) that inherently protect against SQL injection.
5. Least Privilege: Grant the minimum necessary permissions to database accounts used by the application.

Cross-Site Scripting (XSS):

1. Output Encoding: Encode data before rendering it in the browser, using appropriate HTML, JavaScript, or CSS encoding.
2. Input Validation: Validate and sanitize user inputs to prevent malicious scripts from being stored or executed.
3. Content Security Policy (CSP): Implement CSP headers to restrict sources from which scripts can be executed.
4. Escaping: Always escape user-generated content.
5. HTTP Only and Secure Cookies: Use HTTP Only and Secure flags for cookies to prevent access via JavaScript and ensure transmission over HTTPS.

General Best Practices:

1. Regular Updates: Keep all software and libraries up to date with security patches.
2. Security Testing: Conduct regular security audits and penetration testing.
3. Use Security Libraries: Implement security-focused libraries and frameworks.
4. Educate Developers: Train developers on secure coding practices.

Implementing these practices helps mitigate the risks associated with SQL injection and XSS, enhancing the overall security of the web application.