https://www.quora.com/What-is-a-good-approach-for-product-design-interview-questions

Image source: http://bit.ly/1a5FuWX by Sacha Chua

When coaching candidates on product design questions, my favorite approach is the CIRCLES Method™. (From now on, I'll just call it CIRCLES.) I invented CIRCLES and published it in my interview prep book, Decode and Conquer. CIRCLES is a comprehensive framework designed to produce complete and satisfying responses to a design question. Just remember, designers love circles, and the CIRCLES Method™ is perfect for design questions -- whether it's at the product manager or designer interview.

Comprehend the Situation

Many candidates plunge into a design question without understanding questions such as:

• What are we trying to achieve?
• Who are we designing for?
• Why do they need it?
• What constraints do we have?

Urmila Singhal illustrates the importance of "comprehending the situation." She once received an interview question about "designing an airport." She reveals that she got caught up in specifying the solution -- "takeoff, planes, etc." -- only to find out later in the interview that this new airport was constrained to a tiny 100 by 100 square foot plot of land.

That changes things doesn't it?

Identify the Customer

There's no way you can build the ultimate product that does everything for everyone. Companies that try often fall short.

During the interview, you want to propose amazing products, not mediocre ones. Focus on a single customer segment or persona, and you'll increase the chance you'll build a killer product that solves their needs deeply.

So that's the second step of the CIRCLES Method™. List all the personas, and choose to discuss a few in detail.

Report the Customer's Needs

Once we've identified the customer, it's natural to report the customer's needs, requirements, or use cases. In today's world, we're all about Agile environments, so use the lean and mean user story template:

As a <role>, I want <goal/desire> so that <benefit>.