We have been fed the pablum that effective multitasking is one of the primary skill sets of a successful manager, executive, entrepreneur, etc. The needle on my BS meter hits the red line when I hear this. The quickest path to mediocrity is to become a multitasker. Our brains are literally not made to multitask, you are incapable of doing it with any degree of success. When you fight biology, nature has a way of making sure that you lose.
The key to success is FOCUS. The most common complaint that I hear in the workplace and in the personal lives of colleagues, friends, and family is that there isn't enough time. Hogwash. The problem is their use of time. Fiddling away at the edges will not amount to anything but busy work, maintenance, and goals being pushed back - or worse, the debasement of quality.
I have a quick and effective tool for focusing on the right things:
1) Determine what is important right now. This provides clarity and separates that which has value from that which is "valueless" at this point in time.
2) Focus on what you determined to be important. The key is to uni-task, not multitask.
3) Have a bias for action. Be in the present and forget what lies before and behind you, stay focused on what's in front of you right now.
4) Rinse and repeat. Repetition and consistency will eventually drive multitasking from your life and you will become quite proficient at executing those things that have the most value.