How do I improve my mind to college level work?

Im a recent high school graduate and I wasn't a hot-shot or did very well....but yes im trying to take the big leap and prepare myself....do i need to work on 'critical thinking' ? memory capability? thinking outside the box? alot of people say american education and college is a joke too but yea how do i get smarter? i did have ADHD tho not very severe and came out of Special Ed. i know this isn;'t too hard ..