Practically, as the Greeks would say, you gotta spend some time to "know thyself". Some people know exactly what they want to do (i.e. doctor, lawyer, fireman, police). Must of us have jobs that just "fill in the gaps" of the economy, but are important and fulfilling nonetheless.
1) Take some online personality/career tests. There are tons of free ones.
2) Get a book like 'What color is your parachute?' which takes you through steps to figure out how your personality/passions align to certain careers.
3) Find a job that interests you and ask yourself 'why does it interest me?'
4) Take notes on the types of things you did naturally did when you were young (and your current hobbies) and see what patterns exist (i.e. did you like to draw, or build things, or organize games, or figure out puzzles, or fix radios, or read, etc)
5) I'm not telling you to job hop, but if you are young, it's more understandable and doesn't look as bad on your resume, but...try as many different jobs as you can. See what you like and what you don't.
6) Separate imagination from reality. Sometimes experience helps clarify things. Some jobs sound neat but in reality are very different from your imagination. An ER nurse looks cool on tv but it's way different in real life. I always thought being a lawyer would be great, but in reality, many of their tasks are super detailed, mundane, and dry. A lot less creativity than I thought.
7) If you do all this, added to prayer, and you come up with your PERFECT job, sit down, take deep breath and realize NO JOB IS PERFECT. Ha ha. Most people are lucky if they find a job which hits 2 out of 5 'attributes' they like. All jobs are hard work, even for a doctor that loves helping people everyday. Some jobs are VERY fulfilling but take A LOT of hard work to get there. God will help you find what you're meant to do!
Good luck!