Stop talking about how you're so good at multi-tasking!
There's a lot to be said for efficiently doing an excellent job of one thing through completion and then moving on to do an excellent job of the next thing. Schwartz cites a New York Times article with lots of great hard research stats on exactly how multi-tasking slows down overall time required to complete the multiple tasks and causes the tasker to make more mistakes. Schwartz also brings up the point that frequent multi-tasking can wear down workers' overall energy and result in employee burnout.
Most successful employers know this and are looking for employees who can handle prioritizing multiple concurrent responsibilities.
The ability to quickly assess what needs to be done when is really valuable - and seemingly increasingly rare in an ever more wired world. What many employers are seeking in candidates is exactly that mix of discipline, analytical thinking, and foresight to develop and execute a plan for managing all those tasks.
While you certainly shouldn't go out on job interviews telling employers how you can only do one thing, a better thing to talk about is being great at time management, doing quality work, completing tasks on schedule, and adapting to unexpected business needs.
Doesn't that sound a lot better than saying you're a multi-tasker?