A concise, practical guide to approaching system design interviews that teaches a structured methodology for clarifying requirements, estimating capacity, defining APIs, and iteratively refining high-level and component-level architectures. It explains core distributed-systems concepts (load balancing, caching, sharding, replication, consistency, queuing, and monitoring), trade-offs to consider, and scaling techniques, and illustrates them through multiple real-world example problems and end-to-end design walkthroughs. Emphasis is placed on communicating decisions, justifying trade-offs, and preparing for follow-up questions so candidates can present clear, scalable, and reliable designs in interview settings.