What is one thing I can do today to improve my productivity?

Make a list.  Writing it down is preferable.  Use a sticky note or a notebook.  However, since most of us use technology nowadays, type it into the list or reminder portion of your phone.  It can be the simple tasks that need done, such as call insurance agent, drop off a box at the post office, walk the dog, etc.  These simple tasks put onto a list clears them out of your mind and makes it tangible for your brain to process in an organized manner.  Which is better than the alternative of having a dozen random tasks rolling around in your head.

The best part is as you accomplish these tasks, cross them off.  This counts them as done, clears them from your brain, opens up attention span for the next task.  All of this leads to positive momentum, and helps to create a powerful day, week, month, year.