You learn spreadsheet and database software in this program. It can be helpful to learn this software before you begin the program.
Consider participating in an internship. A labor union or large business would be a great place to intern. Check with the labor relations or human resource management department of a business. Because this field deals largely with people, you should try to gain experience working with people from many different backgrounds.
For this same reason, you should take courses in non-business subjects. Good skills in writing, speaking, and critical thinking are needed for advancement in the business world, and especially if you intend to get a law degree.
Some business courses in high school can be useful preparation for a career in labor and industrial relations. However, you should take only a few, so that your high school transcript shows that you are preparing for a demanding college-level program.