Senior candidates drive. Junior candidates follow. Here's how to drive:
Signal transitions: "I've covered the high-level design. Should I explore the database schema, or would you prefer the caching strategy?"
Prioritize proactively: "The most interesting part is the fan-out strategy. Let me explain that."
Acknowledge gaps: "I'm assuming strong consistency here. If that's wrong, the design changes."
Manage time: "We have minutes left. I'd like to cover scaling and failures. Does that work?"
Don't wait to be asked. Propose what to discuss next.