All programming has a lot in common, so the most important thing you can do is any programming at all. If your school offers any classes, try to take them. If you have time on your own and access to a computer with an Internet connection, you can learn a lot on your own. codeacademy.com is a good starting place. Once you've mastered the basics you can start to write simple games of your own. When I was learning to program, first I wrote number-guessing games that were text-only, then I moved on to things like Pong, then side-scrolling spaceship games, and I went from there.
As far as summer jobs, they aren't too commonly programming-oriented for high schoolers (though if you do learn to program you may find people who will pay you a little to write small programs for them), but after high school more things start to become available. If you have some programming knowledge under your belt in college you may be able to get into programs like the Google Summer of Code (https://developers.google.com/open-source/soc/), in which you can be paid to work on Open Source software, and you can seek internships with all manner of tech companies, including video game companies.
Again, the main point is, video game programming has a lot in common with all other programming, so the main thing you want to do is learn to program. Seek out classes (in college the major for programming is usually Computer Science, or CS) and teach yourself if none are available to you yet.
This might not have ended up being too clear. Do you have any questions?