If you are still in high school, there are several things you can do to prepare for a computer science degree. Take all the math courses you can. Math involves analytical skills that will be useful in programming and other aspects of computer science, for example. Take a logic course, if one is offered (pretty unusual for high school). You might want to take some business courses, too. It’s pretty hard to code a program to deal with accounts receivable if you don’t know a debit from a credit, for example. And take your English and speech classes seriously. I wish I had a dime for every computer science student who could not write decent documentation or error messages and could not present their code for a walkthrough or make a marketing pitch for their application ideas.
While it might sound counter-intuitive, I do not recommend taking some programming courses or doing some programming on your own. While that might seem like a good thing to do, I have found that students who do learn a lot of bad habits in programming. It takes a while to unlearn those bad habits and learn the right way to create sound, maintainable code. Most high school teachers were not properly trained in programming. They do the best they can, but they just do not know enough. And if you program on your own, your code will likely be even worse. So, wait until university for that.