A strong answer compares alternatives against the stated goals. For a feed, compare fan-out-on-write and fan-out-on-read using read latency, write amplification, storage, freshness, and celebrity-account skew. For storage, compare relational and document models using transaction boundaries, query shape, and operational needs.

Practice a consistent time allocation: requirements, estimates, APIs/data, architecture, deep dive, and risks. The exact split depends on interview duration, but avoid spending the entire session listing requirements or drawing an overly elaborate diagram.

Finish with bottlenecks, failure modes, observability, security, and a phased evolution plan. Be honest about assumptions and unknowns. A clear, modest design with sound trade-offs is usually stronger than a complicated architecture whose behavior cannot be explained.