Slow database queries can significantly impact application performance, leading to wasted resources and frustrated users. Indexing is a simple yet powerful solution that can dramatically speed up query times by allowing databases to skip full table scans and instead check indexes for matches. However, over-indexing or indexing large, infrequently filtered fields can degrade performance and waste resources. To identify index-worthy queries in your application, start with performance monitoring tools like Sentry that provide an overview of your app's slowest database operations. Then, use your database's built-in diagnostic tools to diagnose problematic queries further. Once you've identified a query that could benefit from indexing, apply and test the index using EXPLAIN commands in SQL or .explain() in NoSQL databases like MongoDB. By focusing on high-impact queries and testing your fixes, you can quickly improve database performance.