The 80/20 rule is one of the most helpful concepts for life and time management. This rule suggests that 20% of your activities will account for 80% of your results.
The 80/20 rule is also called the “Pareto Principle.” It was named after its founder, the 
Italian economist Vilfredo Pareto, back in 1895. He noticed that people in society seemed to divide naturally into what he called the “vital few,” or the top 20% in terms of money and influence, and the “trivial many,” or the bottom 80%.
Later, he discovered that virtually all economic activity was subject to this principle, in that 80% of the wealth of Italy during that time was controlled by 20% of the population.
Pareto’s 80/20 rule can be applied to almost any situation. Understanding the principle is essential to learning how to prioritize tasks, days, weeks and months. In particular, it can be applied to goal setting and productivity.
How Does it Work?
If you have a list of 10 items to accomplish, 2 of those items will turn out to be worth more than the other 8 items put together.
Most people procrastinate on the top 10 or 20% of items that are the most valuable and important, the “vital few,” and busy themselves instead with the least important 80%, the “trivial many,” that contribute very little to their success.
How to Apply the 80/20 Rule to Goal Setting
Here’s what you should do in order to effectively apply the 80/20 rule to goal setting and to your overall productivity.
First, take a piece of paper and write down 10 goals. Then ask yourself: If you could only accomplish one of the goals on that list today, which one goal would have the greatest positive impact on your life?
Then pick the second most important goal. What you’ll find is, after you complete this exercise, you will have determined the most important 20% of your goals that will help you more than anything else.
You should continue to work at those goals that you’ve chosen as the most valuable all the time.
Eat the Biggest Frog First
You often see people who appear to be busy all day long but seem to accomplish very little. This is almost always because they are busy working on tasks that are of low value while they are procrastinating on the one or two activities that could make a real difference to their companies and to their careers.
The most valuable tasks you can do each day are often the hardest and most complex, but the payoff and rewards for completing them can be tremendous.
Before you begin work, always ask yourself, “Is this task in the top 20% of my activities or in the bottom 80%?”
The rule for this is: resist the temptation to clear up small things first.
If you choose to start your day working on low-value tasks, you will soon develop the habit of always starting and working on low-value tasks.
Referenced from www.BrianTracy.com