What steps should I take in high school to prepare for a Computer Science major in college?

Take as much high-level math in high school as you can. It'll help you prepare for the math courses you'll need to take. I'd also recommend taking a few programming courses, but the math is definitely more important. As it comes to summer programs- I'd look to see if the schools you're interested in offer any math or science related summer workshops or camps- talk to some admissions counselors, who will likely have all the information you'll need. That'll give you the opportunity to get an inside look at some colleges and do some networking as well.

You can definitely start building your network now. Look for meetups in your area that tie into your areas of interest, go to company recruiting events and career fairs, just start talking to people who do what you think you might want to be doing in 5 or 10 years. You can start laying the groundwork for finding internships or summer positions. You might find yourself well positioned for your career once you finish your degree!

Harvard actually has a course that they offer (for free!) for computer science which is CS50: Introduction to Computer Science. I highly recommend that you take this course BEFORE you definitely make that decision if you can. I say this because a lot of individuals think Computer Science is one thing and in reality it's something completely different. However, this course will give you exposure to several programming languages if nothing else. I'm not sure when enrollment for it is, it may not be until January but it's well worth taking.

https://www.edx.org/course/introduction-computer-science-harvardx-cs50x

Past that, someone also mentioned mathematics. Take every course you can get near. Algorithms are very important as well but unlikely you'll find courses at the high school level that will teach those. But you can learn a lot of algorithms online. Discrete Mathematics is also very important.

Networking is really a different activity altogether. I'd recommend looking for programming user groups in your area. That's a good start. Meeting as many professionals as you can will help you. Never too soon to start a LinkedIn account as well. That usually how professionals link and network with each other these days.

Good luck!

If you haven't already, start learning how to write code. If your school doesn't offer any courses, there are plenty of online courses. Check out stackoverflow.com for help when you get stuck. You'll probably figure out pretty quickly whether you (a) like writing code, and (b) have a knack for it. If you're already writing code, try experimenting with different languages.

Math is important as well, because it trains you to think in a way that will benefit you in a computer science program in college.

Computer Science is much more than writing code, but if you discover that you don't like writing code, or it just doesn't "click" with you, it may not be a great experience.