How can I improve for college admissions?

I will be a junior this coming school year and I am wondering how much I will need to improve in order to get into a good college. My PSAT scores are: Critical Reading- 53 Mathematics- 47 Writing- 58. This year I advanced to state with a team in my school's agriculture program. Throughout High School, I have been 1st chair in our Concert Band, participated in 3 UIL events, became a member of my church's youth group, was a part of our schools One-Act Play, was admitted into the National Honors Society, and finished my sophomore year with no absences and a weighted 98 average in all of my core classes. I am currently enrolled in all of my school's AP classes and next year I will be taking 3 college level classes and will be writing for my local newspaper. I am interested in a few private universities (especially Northwestern University, as I aspire to become a journalist) but am worried about being accepted. Any tips on whether I am on the right track, my chances of getting accepted, and how I can improve in order to get in would be greatly appreciated.