The most challenging part of college preparation so far has been picking classes. It's really the first taste you get of just how different college is from high school. Before, where there were maybe 50 class choices between all the departments, there are now at least 50 choices per department. And there is no one telling you what classes you should take to get into a good college. You're in college.
The first step is to imagine where you want to go with your life. Yep, big picture stuff right off the bat. You need to do this because some of your freshman courses will be pre-requisites for your major classes later on. Once you've done that, look at the general education requirements you need to fill. Some of those can be covered by AP exams (check this carefully with your school), the rest you will need to fulfill sometime in the next four years.
After you have a general idea of what courses you want to take, it's time to look at the schedule. This is where things get confusing: you jump head-first into your college's computer system, with little or no prep. It'll take a while to navigate your way through the system, but no worries, you'll figure it out soon enough. Find some classes that look good. Note what requirements they fulfill and where they fit in the schedule.
Once you think you know what classes you want to take, map them out. How early on a Monday morning is your Intro Spanish class? (Never have a class before 8:30 if you can help it.) Make sure none of your classes overlap and all that good stuff. By the end of the process you should have a decent schedule (and quite a headache, too).