Most of us intend to be efficient, but few of us actually are because we allow distractions to break our focus. When you are working on something that you have listed on your calendar, you want to focus on that activity and that activity only. That means ignoring (at least for the time being) the blinking message light on your phone, the beep from your email inbox, or whatever else might distract you.
Interruptions can be costly! When someone calls for you and your assistant puts the call through because they ask for you, is that a distraction? Yes! Your calendar should allow you time to return phone calls or emails, but at specific times. Have your assistant screen calls and take messages and schedules phone appointments when needed. If you do not have an assistant, simply record an outgoing message that specifies what times during the day you return messages to avoid these costly distractions.