The best minds of my generation are thinking about how to make people click ads.- Jeff Hammerbacher
When interviewing candidates, I'm surprised how few (especially engineers) do not ask questions back to me to help shape their answers. When I ask most people to perform a task in an interview, they expect I've done a good job thinking through what I want to ask them, and jump into performing on the task. If you're doing an interview, one of the starting points for any problem solving excersize is to gather information and confirm that you've gathered it correctly. This is the true problem solving approach and tends to impress interviewers, even if they don't have any more clarification to give.
When I interview engineers one question I typically ask is a simple data modeling question: "I want to create a database table (or class hierarchy or whatever) that maps who reports to whom in the company. How would you model that?" It's straight forward, but then I get to follow it up with "now our company is grid-based so you typically have both a manager for you skill and a different manager for your product. Can you model that?" The interviewee will make various changes to their model. "Great, but I forgot to mention that we are geographically disperse so sometimes there is also a local office manager in addition." When someone is quick on their feet and can incorporate my changing requirements that's a great thing, but ...
One day I was interviewing someone and after my first task she paused, "okay, we'll let's clarify requirements before we do design." She then proceeded to ask me various questions about the organizational hierarchy and desired performance characteristics. I tried to play dumb, but she was so good at asking she got everything out of me and just had to do the one design which took far less time than me stumbling out each new requirement.
I took that to heart in future interviews that I did myself - when given a task to complete I now pause and ask clarifying questions before proceeding to create the answer. I hope that's helped me too.
P.S. I hired her. One of the best engineers I ever hired.