You can focus on only one thing at a time. That’s what it means to focus: to direct your attention to a singular point.  With this in mind, do you think it better to focus on improving your strength or overcoming your weaknesses?

I say improving your strengths. First, people are typically willing to work harder to maintain and develop skills and abilities they are already good at.  Second, the outcome of focusing on your strengths is usually preferable.  You were hired in part because of the skills and attributes you possess, so improving these will likely improve your performance at the job you were hired to do.

You should give time to turning your weaknesses into strengths, but this shouldn’t be your focus.