There may be 20 colleges you want to attend, or you could have your heart set on just one. When you are applying to college be practical. Most students should apply to somewhere between 5-7 colleges. There are no guarantees that you will be accepted to the school you desire, but you should have a good idea about your chances of admission to each school. That list of 5-7 should be broken down into reach, match and safety schools.
To categorize the schools on your list do your research. You need to know what the admission requirements are and how close your stats are to those requirements. Have you taken the required courses? Are your grades at, above or slightly below the requirement? Have you taken the required entrance exams? How close are your test scores to the schools' typical incoming freshman?
Reach schools are just that, your statistics; grades, and test scores fall slightly below the average incoming freshman. You have a chance to get in but you will be facing tough competition. Match schools are where your statistics fall in the top 25% of the incoming freshman class. Your admittance is not positive, but likely. Safety schools are schools where there is little doubt about your acceptance.
As you select the schools you will apply to think about the level of challenge each of these categories represents. You may have your heart set on the reach school, but if you get in that may mean you'll have to work harder than others to maintain good grades. Can you live with that?
I typically recommend that students apply to two schools from each category, but many students will place only one safety school on their list. The result you want is to gain acceptance at a few of the schools you have applied to. This will give you some choices as you make your final decision. One of the biggest benefits to being accepted to more than one school is that it allows you to compare offers of financial aid. It's important to select a school that meets your needs but it is equally important that you will not graduate with more debt than you can handle.
Being accepted into more than one school gives you options and the opportunity to think about what will ultimately be your best choice. Consider all things, academics, the social aspects and perhaps the most important, the financial aspect. After all, while getting into a specific college may feel like the most important thing in your life, it's your life after college that's really important.