Answer:
All of the above
Step-by-step explanation:
Read a book about careers : could inform you about careers in a specific industry for example (What are the careers in aerospace?)
interview a professional : That professional will be able to give you lots of information about his job but also about related jobs (like the other professionals he interact with on a regular basis)
visit a guidance counselor : a counselor will be able to identify careers that match your interests and skills.
search for information on reliable Web sites: In addition to give you info about specific careers, you might look up for job openings to give you more info about the potential working conditions and salaries.