Embrace this question as an opportunity to talk about your best qualities. It can help to plan and practice your answer to this question - especially if you are naturally modest or shy. Most of your competitors will not hesitate to brag about themselves. However, if you plan thoughtfully, your response can be much more eloquent and effective than the typical braggart's.
To prepare your answer, write down a list of your top strengths and decide which 3 are most relevant for the position at hand. Avoid choosing generic strengths that anyone can claim. Don’t come out with general statements that you're a "hard worker" or "people person." Be specific and prepare an example to demonstrate each strength.
Instead of saying that you're a hard worker, say:
"One of my strengths is my strong work ethic. When I commit to a deadline, I do whatever it takes to deliver. Last week, we had a report due and got some numbers back late from our team in Singapore. I pulled an all-nighter to finish the spreadsheet because I knew that the client needed to receive the report on time."