I have always fumbled with this question as I have nothing to back up my claims. I have little experience so I cannot guarantee that I can bring the company x number of clients per year, or $x of profit annually, neither do I know how profitable I am.
I only have a testimonial letter from my previous boss to backup whatever I say on an interview. The answer I plan to say when asked is, "The compliment people give me most frequently is that I am a diligent, reliable and trustworthy employee." However, I need more details to fill in as most interviewers expect me to at least speak for half a minute, and I don't wish to lie. Other than this, I looked through what teachers describe me as in report cards, but these testimonials are vague, can be used to describe more than 25% of the students in my class and they don't describe me well anyway.
How should I come up with a more detailed answer to this?