I wasn't able to book a room in a youth hostel in advance, so my first night's accommodation was spent on the floor of a friend of a friend. And I woke up too late the next morning to get to the HI Downtown San Francisco hostel in time to book for that night, so I ended up in a Ramada Inn on the second night. The Ramada Inn was nice, but it cost more than four times the price for a bed at the youth hostel. San Francisco is a very popular destination, so book accommodation well in advance.
Similarly, the famous Alcatraz was booked up so far in advance, I'd have had to book two weeks before arriving to get a place on a boat trip to the old prison island. If Alcatraz is a destination you definitely want to visit, then book ahead.
San Francisco's weather was a bit of a shock after sunny Los Angeles. San Francisco is no stranger to cloudy skies and fog, even in mid-summer. The fog particularly likes the Golden Gate Bridge, so I was disappointed to arrive there to be presented with a view obscured by white haze. If you intend to visit the Golden Gate Bridge, check the weather forecast before you set off on foot or pay to join a tour.
The famous San Francisco cable cars are attractive, but the queues at both ends of the cable car route were so long that I never thought about joining them. Instead I took the historic streetcar tram along route F from Market Street to Fisherman's Wharf. The streetcars don't take the hilly routes, they take the long way round, but they make a nice way to travel around the peninsula without having to join a queue.
Even ignoring its better-known attractions, San Francisco is a city with a great atmosphere. San Francisco feels much more crowded and compressed than Los Angeles, but still keeps the laid-back Californian mood.