Good advice above. I am likely to say almost the same thing but in different words. Some important criteria to look for are:
Budget: What can you afford? What can you afford without taking on debt? There are a very large number of very good universities. Many students spend more than they really need to. A college education is the first really expensive item that you are going to buy.
Distance from home: If you live on campus, then attending a university that is 5 miles from home is going to feel like a completely different world compared to living at home. You should think about how far away from family and friends you want to be (but recognize that if you go to university 5 miles from home your friends still might have moved far away).
Size: Would you be more comfortable at a large university or a smaller school?
Academic Rigor: How difficult of a university do you want? Top students sometimes want to go to the highest ranked university they can get into. However, this often means the academically most difficult and challenging univerity they can get into. At MIT or Harvard pretty much every student was top in their high school, but a lot will then be in the lower half of their class at university.
Also important under “academic rigor” as @happy1 mentioned is a realistic assessment of where you will be able to get accepted.
Potential Major: You will want to look for a university that has a good program in your likely major or majors. Many students change their mind about their major after arriving at university. Thus you might want to attend a university that has a strong program in multiple fields that you might be interested in.
Anything else: You are going to be attending classes, doing your homework, taking tests, doing you laundry, and just getting yourself up in the morning. You want to attend a university or college where you are comfortable. This might mean in a city, or in the country, or in an area with mild winters, or in an area that gets lots of snow, or anything else that matters to you.
You should think about what you want. Then visit multiple schools and see what you think when you are there. Most or all schools will give you a guided tour. Many schools will allow you to sit in on class and/or have a chat with a professor in your intended major. You will have to sign up for any of these.
By the way, your original question “What’s a good way to find a good fit” is a very good question. You are starting to think about this the right way.
One more thing that I might add: You need to apply to safeties. You need to find at least one and preferably two safeties that you know you will get into, you know you can afford, and you would be happy to attend. Matches and reaches are usually a good idea but are optional. If your safeties are a very good fit you might not need to apply anywhere else. One of my daughters ended up deciding that she wanted to apply to very good universities that were all safeties for her (they were out of the country in Canada where admissions is predictable largely based on stats). She didn’t need to apply anywhere else. I have seen a few other cases of students that didn’t really need anything other than their safeties because their safeties were that good. Most students also want to apply to matches and reaches.