To be more effective, it is often efficient to improve on your number one weakness.
You could try to improve on your strengths, but there are diminishing marginal returns to getting better. (Usually. Sometimes it’s efficient to truly master a skill, but that’s a topic for another day.)
My number one weakness is premature optimization: I like to do things right, so I invest more energy than necessary to get the result I want. Think of it as a special case of perfectionism.
What’s the number one thing holding you back? Are you aware of it?