In order to be a great leader, it is important to be able to lead yourself first.  This requires a certain level of self-awareness.  Here are a couple tools to help.

16 Personalities.  This is a great tool for a free assessment of yourself as well as insights into others.  It will "help you learn what really drives, inspires, and worries different personality types, helping you build more meaningful relationships".

VIA Survey. "The VIA Survey of Character Strengths is a free self-assessment that takes 10 minutes and provides a wealth of information to help you understand your best qualities. VIA Reports provide personalized, in-depth analysis of your free results, including actionable tips to apply your strengths to find greater well-being."