Start every system design answer the same way.
Minutes -: Clarify requirements. Ask about scale (how many users, requests per second), features (which specific features to design), and constraints (latency, consistency, availability).
Write the requirements on the board. This gives your interviewer a chance to guide you. If you skip this step, you might design the wrong system.
After clarifying, state your assumptions: "I'll assume million daily active users and requests per second at peak."