To know yourself is your first priority!
How can you realistically set goals, go about life and have successful relationships if you don't know who you are or what you want? You really can't.
When we don't know where we are headed it's hard to set goals, get motivated and determine the best course of action. Before we can do any of these things we must establish who we are.
To know yourself:
Be aware of your strengths, weaknesses, likes and dislikes
Observe and be aware of your moods, reactions and responses to what is happening around you
Become aware of how these moods and emotions affect your state of mind
Examine how you interact with others
Observe how your environment affects you.