I visit S.F. occasionally as I have family there. You can have a good time just wandering around the place on public transit, especially the trolley cars. Do some research before you go about self-guided city tours. They'll tell you what buses to take, where to catch the trolleys, and what there is to see/do.
One place I always try to go with my brother or my brother-in-law is:
http://zeitgeistsf.com/ whose motto is unforgettable. It's a site for bike messengers and motorcyclist enthusiasts to hang, and there is plenty of vintage mcy racing memorabilia in the place. They even have some rooms for rent upstairs if you get too-trashed to leave.
Golden Gate National Park and its easternmost-portion the 'Panhandle,' named for its shape, not for what may happen to you while there, ("Spare change, man?") have many features worth seeing. If you go all the way west to the ocean in the park, stop in at Cliff House
http://www.cliffhouse.com/home/index.html for something to eat, and to admire the view. South of that a bit on the park side, is a garden restaurant called the 'Park Chalet.'
http://parkchalet.com/ They have a mini-brewery, and the artwork on the walls is from Works Progress Administration-era artists (the Great Depression), which are filled with all-sorts of hidden messages, social commentary, and depictions of the surrounding area. Look for the motorcycles in the pictures! If you go to the website for the Park Chalet, they have pictures of Golden Gate State Park in-which the property is located. One of those pictures is of a windmill, which is the Queen Wilhelmina Tulip Garden, and is located on Pacific Highway 1, between Cliff House and the Park Chalet. For those of you who are into old rock & roll, and especially psychedelic rock, one of the S.F.-area bands from those times was "Country Joe & the Fish," best known for their social commentary songs of the times, like the "Fixin'-to-Die Rag" and "The Fish Cheer" which came to prominence on the "Woodstock" live album. "Country Joe" is Joe McDonald, and "The Fish" is Barry Melton. If you want to see a guitar solo that smokes, find the movie "Zachariah" which has some parallels to the recent "Cowboys and Aliens" movie. The star in "Zachariah" is a very young Don Johnson as a gun-slingin' cowboy, way-before "Miami Vice" or "Nash Bridges," which was filmed in San Francisco. Country Joe & the Fish play during "Zachariah" and are characters in it. I'm not sayin' it's the best movie ever, but it does have its moments, and watching Barry Melton wail-away on guitar in a bar is worth the rental fee. Barry Melton played at my sister's wedding in San Francisco which took-place at Queen Wilhelmina's Tulip Garden.
Of course, you can go to Chinatown,
http://www.sanfranciscochinatown.com/ Pier 39,
http://www.pier39.com/index.cfm
Fisherman's Wharf,
http://gocalifornia.about.com/cs/sanfrancisco/a/sffishwharf.htm Ghiradelli Square and The Cannery are great places to people watch and to shop/eat, the downtown shopping area, and no trip should omit a trip across the Golden Gate Bridge. You can drive, bicycle, or walk across. Sausalito, in Marin Co., on the other side of the bridge, is 'richer than you are,' but being in the vicinity of the Marin Headlands, there is much parkland to roam especially if you like to hike.
Any veteran will tell you the weather changes in a few minutes, so be sure to dress for changes, bring a good raincoat, layer clothing, and just like on a bike, if your head and hands are cold, the rest of you will be too. A knit cap is easy to carry and you can always jam your hands in your pockets if you have a warm outercoat, otherwise, bring gloves.
San Francisco is all about the tourists, and generally you will find people approachable and helpful. Just be aware of your surroundings, and consult some sources of tourism information, and decide what you would like to do most.
I do recommend the Alcatraz trip if you like history, last time I went, we had a live guide rather than a taped (now podcast?) self-guided tour. It is a great place to visit, better doing it earlier in the morning rather than an afternoon trip, my choice. I think it is the Grey Line who runs the excursions there (the boat).
Watching the afternoon fog come-in off the ocean and across the bay will give you your $'s worth for atmosphere, and will probably chase you into one of the great restaurants the city is known for, in-order to get warm and fed.
Just plan things out for what you are interested-in most and don't worry about strictly-adhering to the schedule. And, if an eccentric fellow offers to escort you to "The Tenderloin," he's not going to take you to a great steakhouse!:rofl_200: