Career manuals abound with ways to tackle this question. And most of them seem to suggest that you should take one of your strengths and portray it as a weakness. For instance, I work too much. But this will actually work against rather than work for you because it may imply that you do not organise your workload effectively, or that you have poor time management skills. Instead, opt for a genuine weakness.

For example:

I used to struggle to plan and prioritorise my workload. However, I have taken steps to resolve this and now I have started using a planning tool and diary system on my laptop.