Typically, we're happiest doing something that is congruent with our personality type and interests, that we are passionate about, and that holds some intrinsic meaning for us. A career counselor or coach will probably suggest you take the Self Directed Search, which is interest-based. It's available online at:
Welcome to the Self-Directed Search...the world's most widely used career interest inventory!
The result is a detailed report. It costs 9.95USD to take the report, and you get the results immediately. You get a three letter code with jobs associated with its various permutations. Research has shown that people with a certain three-letter type tend to have high degrees of satisfaction in certain careers, and these are provided in the report. Associated with each career suggestion is a DOT Number: you can go to the following site, enter the DOT Number, and read about the career - what it's like, job prospects, education needed, etc.:
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Another common approach is to look at the kinds of careers that provide the best fit for one's personality type. This is a book many career seekers I've known have found helpful:
Amazon.com: Do What You Are : Discover the Perfect Career for You Through the Secrets of Personality Type--Revised and Updated Edition Featuring E-careers for the 21st Century: Books: Paul D. Tieger,Barbara Barron-Tieger
I agree with CaptainRich that the military is a great career option - however, you've mentioned the military and nursing in your post. That's quite a spread. What appeals to you about these options as careers, other than that they're there as options? Unless you find yourself getting excited about a career when you read and think about it, you're likely to find yourself unhappy with the choice eventually, in my experience. Do what you love, and (as the saying goes) you'll never work a day in your life.
Vasily