You have to decide what your highest priorities and have the courage--pleasantly, smilingly, nonapologetically--to say "no" to other things. And the way you do that is by having a bigger "yes" burning inside. The enemy of the "best" is often the "good."

Keep in mind that you are always saying "no" to something. If it isn't to the apparent, urgent things in your life, it is probably to the more fundamental, highly important things. Even when the urgent is good, the good can keep you from your best.

Stephen Covey, The 7 Habits

[Spending time on things that are not urgent but important] is the heart of effective personal management. It deals with things that are not urgent, but important. It deals with things like building relationships, writing a personal mission statement, long-range planning, exercising, preventive maintenance, preparation--all those things we know we need to do, but seldom get around to doing, because they aren't urgent.

Stephen Covey, The 7 Habits of Highly Effective People