As someone who has struggled with focus throughout my life, I’ve known for a long time that our brain can not actually multi-task. There are certain mundane things we can do without thinking about, like eat, or keep our foot on the gas pedal etc, but as far as work and dealing with people we don’t actually multi-task. We switch back and forth between the 2, or 3 things. (Hopefully not more than 3 because even 2 things makes it take longer.)
I have recently enjoyed learning some great tips from Dave Crenshaw. Watch one of his videos here and apply it immediately. Make sure to the do the 1 minute exercise he takes you through in the video. You might be shocked at the results.