Knowing what you want to do in life starts by asking yourself the right questions. Don't waste another day of your life wondering what you should be doing. Ask yourself these questions and let the answers guide you to the good life as God intended for you.
What Is Your Personality Type?
I believe knowing ourselves is the first step to understanding how we can live the best life possible. When you know your personality, or the psychology that makes you who you are, you then have powerful knowledge that will help you avoid spending time on pursuits that don't fit with your makeup.
One of the easiest places to get started with understanding your personality type is a website called Human Metrics. They offer a Jung Typology Test and a Jung Career Indicator all for free. Dr. Jung is the scientist behind the Meyers Briggs personality test. The typology test on Human Metrics is an abbreviated version of the Meyers Briggs. I highly suggest you take both tests to better understand what makes you tick.
What Are Your Strengths?
As Peter Drucker says in his book, Managing Oneself, you cannot build upon weakness. You can only build upon strength. Knowing where you are strong will help you to focus on the most effective actions that will get you to your life goals. It will also help you avoid wasting precious time trying to improve weaknesses that you probably cannot develop beyond mediocrity.
For example, knowing my personality (ENTJ) and my strengths (leadership, strategy, personal development) allows me to focus all my energy on activities where I'm more likely to win. I'm not a very strong nurturer. If I spent a bunch of time trying to develop my nurturing skills by working at a nursery, I'd find years later that I was only a mediocre worker who wasted a bunch of time. Time I could have used to have a better impact on myself and the people in my life.
If I Put a Gun To Your Head and Told You That You Could Only Pick One Thing To Do Today...What Would That One Thing Be?
This is a slightly extreme question, but it's designed to prove a point. I believe most people know deep down what they want to do. They are just sometimes afraid to do it because it's not "safe."
You've probably been taught all your life that you have to go to school, then go to college and then go get a safe job that will pay the bills. That's how I was raised. I'm sorry to say that our parents and teachers didn't get this one right. I'm not saying college is a bad call in and of itself, but it will be a six-figure nightmare if you pick the wrong major in an attempt to just "land a good job." You will be miserable and marginalized for as long as you follow that path.
So if you could do anything with your life, what would it be? When you can answer that question, you will know exactly what you should be doing. Then you can build an education and training strategy around that goal.
Who Are Your Mentors?
Trying to be John Rambo is going to lead you to a crap life. Period. If you want to accomplish anything in your life, you better seek out people who've already done it so that they can guide you and shorten your learning curve.
Do not skip the step of finding a mentor who can help you get to where you are going. No super-successful person in the history of earth has reached the top of their game without a mentor to guide their efforts.
Now that you have a better idea of what you should be doing, it's time to take action with the answers you've discovered. Take every personality test you can get your hands on. Take the Career Indicator test I linked above. Focus on building your strengths and spend very little time improving weaknesses. Begin pursuing what makes your heart come alive and find mentors that can help you win as you move forward.