Don't know where you'll be staying at but I agree with the above - depends on what you're into, but the observatory is awesome! I will add that if you want a more chill beach experience than Venice (which is also cool just too many people for me), I always point people to Angel's Gate in San Pedro. Cool overlook, there's a path to the beach (rock beach though) and less people.
Haven't lived in LA for a few years but I grew up and went to school & worked all over so if you have specific questions, ask away.