Knowing your own strengths and weaknesses gives you a better understanding of yourself and how you function. Your weaknesses are not your downfall, they are areas you need to develop and build.
In order to use your strengths and improve on your weaknesses, you first need to know them. There are several ways of identifying your strengths. Ask for feedback from those who know you well, they interact everyday with your strengths and weaknesses. Learn from school projects and summer job experiences. Get to know people who have chosen a very different life than yourself.
Understanding your strengths helps you to grow more and keeps you ahead in a lot of things. They also will get you recruited and enable to recognize career development possibilities.
Knowing your weaknesses gives you a clearer understanding of things that may be holding you back, and you can then learn ways not to let them prevent you from going where you are aiming at.
Here are self-assessment exercises about your qualities. Complete the exercises in about 45 minutes.