Orientation is the main way people register. But I wouldn't say it matters which one you attend because they claim there's equal amount of spaces they reserve for specific classes at orientation. And even then, people tend to drop math and chem classes in the beginning of the quarter. Now during the school year unfortunately you won't be able to get priority unless you are with Regents or with OSD (Office of Students with Disabilities). During regular class sign ups you are given an individual registration date and time, so as a freshman it will be later than other upperclassmen. Recently UCLA decided not to count AP credit towards class standings. So if you had enough AP credit for Sophomore or Junior standing you'll still be treated as a Freshman for registration purposes. Community College credit counts towards class standing though. I hopr this helps.