With some practice and awareness, this can easily be mastered. When posed a design question (which will usually be vague and ambiguous), it’s important to ask relevant clarifying questions to reduce the ambiguity and not make any assumptions on your own.

Also, it’s important to drive the conversation in a structured way (especially for more senior candidates).

Here are some of the points to keep in mind, that the interviewer is evaluating:

• Clarifying questions to reduce ambiguity.
• System requirements (functional and non-functional).
• Quantitative analysis.
• Structured and organised approach.
• Constraints and edge-cases.
• Product awareness.
• End-user understanding.

Usually a successful candidate analyses the problem space in a structured manner, showcases organisation and logical ordering of different topics, clearly listing the requirements, focuses on important areas of discussion, does trade-off analysis and draws example from past experience (wherever applicable) and talks about the common pitfalls in development.