Been to or live in San Francisco?

I plan to go to a school there this fall and was just wanting anyone who lives there or has been there to give me the dish on the city. Lemme know your favorite hang outs (keep in mind I’m 18), favorite/cheap places to eat, etc.
Is there anything that I should know about the city?
How about cheap areas to find an apt or room? My school charges WAY too much to live on campus even for SF.
Thanks!