What extra classes and activities should you do/take in highschool to be accepted to a good school for a psychology major?
The same thing you would do to get accepted into a good school for ANY major: take the most rigorous classes your school offers, get good grades and do well on standardized tests. As for activities, do what interests you, do it in depth and with a commitment. Whether it’s a sport, a musical instrument, school government or academic competitions, it should reflect your passion and personality.