Mark Twain once said that if the first thing you do each morning is to eat a live frog, you can go through the day with the satisfaction of knowing that is probably the worst thing that is going to happen to you all day long. Your "frog" is your biggest, most important task, the one you are most likely to procrastinate on if you don't do something about it. It is also the one task that can have the greatest positive impact on your life and results at the moment. The key reaching high levels of performance and productivity is to develop the lifelong habit of tackling your major task first thing each morning. You must develop the routine of "eating your frog" before you do anything else and without taking too much time to thing about it.
This is another way of saying that if you have two important tasks before you, start with the biggest, hardest, and most important task first. Discipline yourself to begin immediately and then to persist until the task is complete before you go on to something else. Think of this as a test. Treat it like a personal challenge. Resist the temptation to start with the easier task. Continually remind yourself that one of the most important decisions you make each day is what you will do immediately and what you will do later, if you do it at all.