During my college decision process, I went through a lot. I know many of my friends also went through something similar. The process for me, although stressful was incredibly enjoyable. I questioned the school I decided to go to for months, and then I finally came to the realization that it was perfect for me and there was no turning back after that.
The best advice that I can give you is to start your college search as early as possible. I suggest that you should have a few ideas on schools you like by the end of your sophomore year. I knew the school that I will be attending (The University of Alabama) was a school I liked my freshman year, and kept that school in the back of my head the entire year. Once sophomore year started, I researched their admission requirements, and prepared to take my ACT. I also suggest taking the ACT or SAT your sophomore year, and then retake it throughout your junior year if necessary, taking the June ACT is the best time to take it, in my opinion.
During my college search process, I used many websites to help me find the right school for me. Collegeboard.org was the main source I used. I also loved using cappex.com after I found a school that appealed to me. I would get recommended schools from college board and then go on cappex and compare them, by campus size, campus life, cost of attendance, etc. You can import all of your test scores and gpa into the cappex system and they will calculate your chances of getting in, but the best source to go through for that is off the actual school website. These two sources helped me immensely, but other good sources are your guidance counselor, and regional recruiters from the school you are interested in.
Your junior year of high school is definitely the most intense. I spent a lot of that year not only stressing out about my classes, but also preparing myself for college applications. I thank myself everyday for doing that, especially since I applied to ten schools, it made the actually application process a lot less stressful during my senior year. If the schools you are interested in, require you to write essays, google practice essays to prepare yourself. Alabama's application was by far the simplest application I filled out, so if you are interested in Alabama, do not stress about the application too much, there is not an essay to write, and you just fill out basic information about yourself.
Ultimately, when you make your decision, you need to go where you feel happy. For me, Alabama felt like home the second I walked onto that campus. I felt like I fit in there, and I knew in that moment that I had to be there. I literally cried. When you get that feeling, you know it is the right place for you.