Choose an accomplishment that is relevant to this job and employer and, preferably, relatively recent. Consider discussing accomplishments that resulted in positive feedback from a colleague or a client/customer. Take some time before the interview to analyze the job description and other information you can find out about Facebook from their website, articles, and other employees. Consider which of your accomplishments fits best with this job and this company, and discuss that example during the interview. Don't ramble while describing your accomplishment, and don't include irrelevant details.

"My greatest professional achievement was turning around the success of my last employer's Marketing department. When I joined, the entire team was struggling, and we were failing to hit our quarterly goals. They hired me to create a new marketing plan, which I designed and implemented without any guidance. Within six months, we were achieving 20-25% above our goals, and my marketing plan brought in an additional 3 million in revenue for the company through the second half of last year. This additional revenue brought the company from an operating loss each quarter to profitability."

"My greatest professional achievement was completing my Bachelor's degree in four years with a 3.9 GPA. I had no financial support from my family and had to work a full-time job while pursuing my Marketing degree. That taught me to prioritize my time, build great organizational habits, and stay focused on my goals. I'm proud of this accomplishment, and I feel that what I learned will give me a big advantage in my career now."