Compare your grade-point average and test scores with the average scores for applicants at the schools on your list. Your GPA and test scores are important for getting into college, but you need to be realistic. If there is a very large gap between you and other applicants, you should think about eliminating that school.
Visit the schools on your list. A school that looks great on a website might not be as great as you thought in-person. Schools typically offer student-led tours, allowing you to ask questions. If you visit during a weekday, you might even get a chance to sit in on a class or sleep in the dorm to get better insight into what it would really be like to attend the school.
Write out the pros and cons of each school. For example, one school might be easy for you to get into and have a program that you're interested in, but the location is not ideal. Though you probably have all these pros and cons knocking about in your head, writing them on paper can help you visually see which ones might not be the best fit. Eliminate schools that have a very long list of cons.
Factor in the costs involved. It's easy to compare schools by tuition alone, but remember that that's not necessarily what you'll pay. A more expensive school might be able to offer you more in terms of financial aid. Remember to include other costs, like travel, and to consider whether you'd be willing to reduce costs by living at home. At this point, it's too early to know exactly how much financial aid you'll receive, but it might be safe to say that a school all the way across the country will be prohibitively expensive. Eliminate any standout examples.
Review the course catalog for advanced classes, particularly in the subject you hope to major in. The introductory offerings are similar at most colleges, and while those might be the ones you're most interested in as a high school senior, you need to look toward the future. Consider the types of classes that the school offers at the more advanced levels. For example, some schools might have professors with a specialty in the exact area that interests you. If the course offerings don't excite you, eliminate that school.
Balance the schools on your "keep" list. You should have some schools that you'll definitely get into, some that are a great match academically and some that would be great to attend, but might be more challenging to get into. The College Board calls these "safeties," "good matches" and "reaches" and recommends having one to two safety schools on your list, two to four good matches and one to two reaches. Find a good balance for you. For example, if you notice that your list is currently heavy on the safety schools, focus on eliminating all but a few of those.