"So what I do now is to pre-empt that by making the up into a virtue, and telling funny stories about how crap I am before people have a chance to notice it for themselves and think maybe I haven't realised"

In this quote, Emily Mortimer is suggesting that she has learned to take control of her own story by turning her perceived weaknesses into strengths. She does this by being self-deprecating and informing amusing stories about her own shortcomings before anyone else has an opportunity to observe them. This is a way of taking ownership of her own narrative and presenting herself in a favorable light. By doing this, she has the ability to manage how she is viewed by others and prevent them from forming unfavorable opinions about her. This quote is a suggestion that we all have the power to shape our own stories and control how we are seen by others. It is a reminder that we must take ownership of our own narrative and utilize it to our benefit.