For this question it’s important to come across as serious and capable, but not too extreme or consumed with work. That might lead the interviewer to thinking you’re unbalanced in some way.
A popular style of answer to this question has been:
“I’m a workaholic, I’ll stick to a task for a long time, hour after hour, to get a good result. I believe in completing work at or above the desired standard.”
While it’s overall a good answer, the word “workaholic” carries a negative connotation – someone who works to the detriment of other aspects of a healthy life. The same answer can be given without the negative word.
“When something has to be completed, I complete it. But it’s not rush, it’s attention to detail and to quality – it’s not just a job done, but a job done well.”
Your answer should reflect your strengths, while overall emphasizing the qualities of a good employee.
“I plan well, so I always make, and often beat deadlines without a loss of quality.”
“I’m first in line for projects and new responsibilities. I don’t mind extra work if it means I can contribute to overall success.”
“When I promise something you may as well write it in stone, because for me a promise made is a promise kept.”
“I lead by example. People who work for me know I don’t tell them to do things I’m not willing to do myself. And I prove it by doing things, not just with stories about things I’ve done in the past.”
“I’ve always been a top performer, from school to my first job to the present. It’s not that I’m smarter than other people, but I put in a lot of extra effort and clearly define goals so I can meet and exceed them.”
“I’ve never called in sick, always met deadlines, and according to past bosses my performance has met or exceeded expectations. My last boss told me I work like the sun rises and sets, every day, without fail.”
“I like to plan things, and stick to a plan, but I know that sometimes the best plan needs changes on the fly. It’s actually part of good planning to be flexible.”
The best answers touch on many elements.
“I take what I do seriously, and I enjoy meeting the challenge every day by planning, working with the team, and finding creative solutions to problems that arise on the way.”
This answer was one of the most clever ever given. “Hire me and see for yourself.”