This is an opportunity to share your accomplishments. Think of a time you stepped outside your comfort zone and took on more responsibility. Improving upon a new skill is an excellent example of a growth opportunity. Another way to answer is to set higher expectations for yourself than others might. This way, you demonstrate that you are an overachiever.

I think they'd say I should go easier on myself. I tend to be a bit self-critical and hold myself to a higher standard than anyone else. I always feel like I can do more. For a while, it was so bad that I was turning in work late even though the work was done on time. I just refused to turn it in until it was beyond perfect. I don't do that anymore, but I still push myself too hard sometimes.

If you have a relationship with your old boss that bridges into your personal life, be careful how much you share. It's great to share how well you get along with your superiors and your team. However, coming across as a sycophant shares nothing about your work ethic.