Write it all down. Put everything on one list. Determine which tasks are easy and which are more difficult.
Do some easy things. Spend 15 minutes doing the easy tasks. Focus on speed: make the quick phone calls, shoot off the brief emails. Cross as many tasks off the list as you can.
Turn to a bigger task. Turn off your phone, close all the open windows on your computer, and focus on one of the more challenging tasks. Do this for 35 minutes without distraction.
Take a break. After 35 minutes, take a 10-minute break. Then return to step two.