Also known as the Pareto Principle. This is a powerful concept that can transform the way you approach your business strategy.
Not enough people apply this principle to their time as a whole - when in stage one, make sure to also track your time.
Toggl is a great free way to do that easily.
Knowing what your spend your time on helps you identify what 20% of tasks actually lead to the best results (both in terms of business results like revenue and life results like happiness)
Pareto's priniciple is my mantra.