Sartre is one of the most celebrated philosophers of his time, and his belief was that every person is the sum total of their actions.
The person I am today, the person I was this past week, the person I was for the previous ten years, are all different versions of me, because they are collections of different actions. It is then simple to identify what we need to do in the future to become who we want to be, by asking:
What are the sum total actions that the person I want to be would take?