2.1
Answer strategically.
In your answer to "What are your weaknesses?", it's important not to mention a real weakness. In other words, you want to mention a skill or trait that is not critical to the position you are interviewing for.
For example, if you're applying for a job in customer service, you do not want to mention that you "don't have great people skills." Furthermore, you should not select a random weakness, e.g., "I'm a perfectionist," which could come off as too scripted.
2.2
Give an example of how you have used this weakness to grow professionally.
Your "weakness" should be an example or story of how you have struggled with an aspect of work, and how you corrected or overcame that weakness in your professional life. This tells your employer that you're a good fit for the role by emphasizing your ability to find solutions to problems.
If you are actively working on overcoming a particular weakness, be sure to explain your plan-of-action during the interview.