Use a repeatable sequence: (1) clarify functional requirements and out-of-scope items, (2) identify non-functional requirements and SLOs, (3) estimate traffic, storage, and bandwidth, (4) define APIs and data models, (5) draw the high-level architecture, (6) deep-dive into bottlenecks and consistency, and (7) cover reliability, security, observability, and trade-offs. Adjust depth to the time available.