Our body of knowledge now doubles in less than 2 years. Your degree may not last much longer if you don't seek additional education. So says Peter Drucker. And like education, it's won't be a one time effort. Instead, self assessment becomes a cyclic requirement, and your guide as you navigate all those careers and jobs.
Self assessment is only half the picture.
To get it really right, you have to have something to compare your self assessment outcomes to. Get Steven Covey's book, The 7 Habits of Highly Successful People, and if you don't do anything else, do what Covey suggests in terms of formulating your personal mission and vision statements. When you get those done, tape them to your bathroom mirror so you see them every day. And alongside them, tape your personal goals. You'll be surprised how powerful this can be in terms of accomplishing what you want to do.