It's probably not your fault if you still don't know what you want to be when you grow up. Reasonably, you assumed school would help you figure it out.
Alas, instructors live in an ivory tower, so most are ill-suited to helping you find a career. And even most students who go to their school's career center leave still unsure what they want to do.
This is a better approach:
Step 1. Scan annotated lists of careers in such guides as the online Occupational Outlook Handbook, or my book, Cool Careers for Dummies.
For even more under-the-radar but currently in-demand careers, go to indeed.com and search on a work-related skill that you'd like to use in your work, for example, writing, analyzing, organizing, selling, or programming. Pick out the one, two, or three careers you find most intriguing.
Step 2. Google the name of that career and the word "careers," for example, "geologist careers." or "writing careers." Read a few articles that seem on-point.
Step 3. For any career that still seems interesting, search Amazon for a book on that career. In the best such books, each chapter is a different person's report on what it's like in that career.
Step 4. For any career that's still of interest, job shadow at least three (one or two might give unrepresentative perspectives) people in the field. Find them in the Yellow Pages, on the website of the profession's professional association, for example, The American Optometric Association (www.aoa.org), your alumni association, or simply ask your in-person or LinkedIn and Facebook networks for referrals.
While you're job shadowing, ask questions such as, "What's your typical day like?" "What ends up being most important for success in this career?" "Why might someone leave this career?" and "What's the best way to get training so you're excellent in this career?"
Step 5. If a career still sounds good, choose it, even if you're not sure. Otherwise, you may be waiting for Godot. Career contentment usually only comes after you've entered it and, like a great-looking suit, tailored and accessorized to fit you.
For example, career coaching fit me only moderately but I now love it, in large measure because I adapted it to fit me: I made nonnegotiable that I'd work from home and that I'd be a more active participant in sessions than the typical counselor who mainly just listens. I also stayed committed to getting better and better rather than giving up after a couple of years of mediocre performance.