Plugins often store data in WordPress databases. Use options API for simple settings, postmeta for post-related data, and usermeta for user data. Create custom tables only when necessary for complex relationships. Index your columns appropriately for performance. Query posts efficiently using WP_Query with proper arguments. Cache frequent queries to reduce database load. Use transients for temporary data storage. Avoid N+1 query problems by fetching related data in single queries. Monitor your plugin’s database performance. Proper database design and optimization ensure your plugin scales well with growing content.