Take anything related to Information Technology - even if you want to be in another area of business. By understanding the technology that drives the applications you will be using, you will be a greater value to your company. See if there are junior colleges which will give you college credit AND high school credit.
I have worked within enterprise companies for many years. The business managers who understand what they need get the better tools, versus rely on IT.
Of course, learn organizational structure, different types of industries. Business is such an open area. There is operations (how the business functions on a day to day basis); management (how to get the best performance out of your employees), human resources (benefits for employees), senior management....financial, IT, leadership in sales, operations, etc.. Again, if your high school does not have general business courses (and I am not speaking of typing)...go to your junior college.
There are many high school clubs and organizations, like Future Business Leaders of America, that you may be able to join at your school to learn more about business and make connections. I was in FBLA in high school and it was a great place to learn more about business, participate in competitions, and make friends.
It would also be useful to take any business curriculum classes that your school may offer. It is also a good idea to take any computer or programming classes your school offers. Regardless of what type of business career you pursue this will be a huge help. Talk to your guidance counselor for more resources at your school specifically.
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