WordPress provides the wpdb class for database interactions. Use wpdb prepare for all queries with variables to prevent SQL injection. Methods like get_results, get_row, and get_var retrieve data efficiently. The insert, update, and delete methods simplify common operations. Create custom tables only when necessary, prefixing with wpdb prefix. Handle database errors gracefully using wpdb last_error. Always consider database performance and optimize queries. Use transients for caching expensive database operations. Remember to clean up custom tables on plugin uninstall. Proper database handling ensures reliability and scalability.