Check out this article:
http://www.macinsiders.com/showthread.php?t=1709 4
I go through the basic steps you can take when choosing courses that will hopefully make it easier for you.
Also there is a download link to the MacInsiders Timetable sheet that is a Word Document you can fill in with your choices to easily map out conflicts
before going into SOLAR.
If you're wanting to plan ahead early to work out all your course list then go through those steps (ONCE THE MASTER TIMETABLE COMES OUT) and you'll be all set.
As mentioned before, make sure to have at least 2-3 backup elective courses chosen incase they are full when you try getting into them on SOLAR.
REMEMBER: SOLAR HAS A TIME LIMIT. And it is very short. So you can't go into SOLAR without anything planned and expect to sort it all out then because solar only lists the course codes, not the descriptions and other things you need to read before choosing the courses. And if you're playing around without a clear plan, your time will run out and you'll have to start all over again!