It's a good idea to have a few careers in mind before choosing subjects. If you're uncertain about this right now, then select subjects that will keep several career options open to you.
Your school Careers Advisor or Pathway Planning Officer will be able to help get you started.
To make sure you pick the right subjects, you should investigate the pathways you can take to get a job in the area that interests you. Once you know these, you can select the most appropriate one for you.
You can learn more at My future and Good Careers Guide.