There are various formal and informal ways of knowing your strengths and weaknesses.
One is by taking a feedback from your near-dear ones. They will certainly tell you what you are good at and what you need to work on.
The other is by trying out various activities and then seeing for yourself what is it that you need to work on.
But both these methods will tend to get a little biased after a point in time.
While we talk about a career the only unbiased means of knowing your strengths and your development, is taking the career test. The test will help you to know your interests (likes and dislikes), aptitudes (your potential) and personality (your work values).
The career test also gives you a profile with all these reports and the career recommendations according to the profile.
Hope this helps.