Not a local or pro, but here's what I did. I didn't have a whole day like you might.

Rode the trolley to and from fisherman's wharf and walked around a bit. Ate at the wrong place there so I won't recommend anything.

Walked china town. That was worth it.

Jogged from the hotel down past the piers and most of the way to the Golden Gate Bridge and back. That was really cool.

Wished I had time to rent a bike and cross the golden gate bridge. Wished I had time to rent a car and go to the Muir redwoods.