But you'll make much greater strides in your performance if you concentrate on becoming more effective.
Effective means that you do the best things, those things that will get you the greatest return on your investment of time. Learning to say "NO" to a small customer so that you can invest more time in a larger one, for example, is a way to become more effective.
Back to our example of calling on your cell phone while you are driving to your next appointment may be efficient, but if you are calling an unqualified prospect, and driving to an appointment with a customer of tiny potential, it doesn't matter how efficiently you do those things, they are still the wrong things to do.
Here's a simple exercise to help you make major strides forward.
Several times in the course of the day, stop what you are doing, and ask yourself this question: "Am I doing, right now, the most effective thing I could be doing?"
If the answer to that question is "No, I'm doing this low value, low return stupid little thing," then stop what you are doing, and do that which is your more effective option.
You'll be amazed at how quickly you'll begin to see improvements in your performance -- you'll work smarter, not harder.