I scored around a 1450 on the SAT by focusing on mostly on practice exams (ask your school for specific resources). I also retook the SAT a few times until I got the score I wanted. When practicing, make sure to time yourself and take note of concepts you struggle with. Your involvement, community service, and GPA often matter much more than just your SAT or ACT score, so make sure to focus on those things as well. Good luck!
I received a score above a 1450 and I did this primarily through prep classes as I was not motivated enough to self study. In fact, I was barely motivated to go to workshops and greatly regret not going to more. Don't do what I did. If you sign up for SAT or ACT prep classes, make sure you attend not only those that are required, but go to any workshops offered that highlight areas you struggle with. If prep classes are unavailable to you, I recommend purchasing self-study books and answering as many practice questions as possible. Khan Academy is also a fantastic resource that, last I checked, offers many free resources for standardized test preparation. If you struggle with the motivation to sit down and actually prepare by yourself, set an hourly goal each week and try to hit that goal. Even something as small as 1-2 hours can make a big difference in score, and that's typically very doable for most students.
To specifically answer your question, I took prep classes 1-2/week for two months for two summers and went to a handful of workshops and I got above a 1450, but I don't think my score reflected my true capabilities at the time. When I was taking diagnostic exams during the prep classes, I was scoring at a near perfect score, and the first time I took the real SAT I scored a 1460. Some of that is testing environment, but most of it was because I hadn't kept up with practice between the summer classes and my test date. It depends on the kind of student and test taker you are, how many hours you will need to put in to score above a 1450. In the grand scheme of things, I didn't put any hours in outside of the 1 hour 2/week prep classes each summer and still got above a 1450. But I should have done better than I did. I think a solid 1-2 hours a week of practice in the months I didn't have the prep classes leading up to my test date would have improved my score 50-100 points. My recommendation is to practice as much as is reasonably possible for you, and make sure you do a few full length practice exams so you know what it feels like to do the whole test at once.