This has an academic side—take the most rigorous classes you can, get the best grades you can, be involved in your education. But just as important at this point are the social and emotional sides. You’re easing your way into a new and exciting (and challenging) place. You’re going to have missteps, and you’re going to change your mind about things. That’s normal, and that’s fine.
This is a tough line to walk senior year. On one hand, you really ought to be shifting your focus to next year. You have a lot of big decisions to make, and you need to allocate time and resources to working on strong applications and making informed decisions. Your daily high school homework isn’t quite as compelling as it was a year ago. On the other hand, you also need to be preparing yourself to be a good college student, and the best way to prepare for college is to be a good high school student.