Hi!
A general approach that most people use is the safety, target, reach model. Firstly, you decide the number of schools that you're applying to, for most people this is typically between 13-18 (but there's no standard number). Out of those, you'd take 4-5 reach colleges (these would be elite schools like the Ivy Leagues, Stanford, MIT etc). Then you'll have about 4-5 target schools (where your scores and grades fit within their typical ranges and with a higher acceptance rate) and the remaining will be safety schools, where your scores are higher than the typical range and where you wouldn't mind going to if all else fails. You can generally find out what these schools should be through the Alma Matters website, filling in our survey where we'll send you a list of colleges or consulting the colleges websites themselves as well as talking to older students at those different colleges to get a sense of the college.
Good luck!