Tips for LA/San Diego/San Fransisco?

Hi all! I’m excited to go on my first ever trip outside of Europe which will be California for 3 weeks! I’ll visit Los Angeles, San Diego & San Fransisco. Anyone in this sub who has any light on any of these cities what’s an absolute must for example? Of course I want to visit Hollywood and the Golden Gate bridge, cliché tourist stuff ;) but I don’t mind some gems that would be a need to explore. And any tips in general would be appreciated too as I am a bit anxious about travelling outside of Europe for the first time haha :) I won’t stay in hostels (except in SF) as my friend will host me in LA and SD but since she’ll work somewhat during this period I will explore some stuff alone. I am currently making up my list as the trip won’t be until July