Ok, I actually live here for about 3 years so far and since it's a very popular tourist site I will do a review of this city for those who are interested in visiting the place. it'll be a long review for sure so I'll only do downtown area for now and the others later.
The best time to come here would definitely be during spring and summer. During the summer there will be street events going on so you definitely do not want to miss those! The weather is best during this time, but please don't stay in August because the fog will take over and you don't see the sun till later in the day. Unless the fog is what you came here for then August is the best time for you to see. The only good thing about the fog is that it'll give you amazing pictures when you go on the ferry boats and see the bridge. The weather doesn't get too hot, it never goes any higher than 80F and its mostly in the 50s all year long. If you arrive in SFO airport, there's a subway station (called BART) in the airport that you can take to downtown SF if you don't want to pay for taxi. It's a 30 minute drive from the airport to SF so the taxi cost can come up to almost $50. Try using the airport shuttles if you don't want to pay alot or don't feel like carrying your luggage in public transportation.
There's alot of hotels here, from big name ones to less known ones. The big name and expensive hotels will be on Market st (Four Season), Stockton st. (Hyatt), Powell st (Francis), and Mason st (Hilton). There are many small ones for cheaper prices all over nob hill. Of course Nob Hill is on a hill and on top of this big hill are probably the most expensive hotels and very classy! There's a Grace Cathedral church there and it's worth taking a look. This area is really safe so its a great place to walk around late at night by yourself even for the ladies. On Post St. there's a burger place called "Pearls" that is voted for the best burger in the city. It's hard to find because it's small but its worth getting their burgers! Try their chilli cheese fries its YUMMY! On this street you'll find alot of Thai reatuarants too. King Of Thai Noodles is one of the best Thai places, but it's cash only. There's Japanese restaurants all over the city too. If you want a really fancy dinner, on Sutter st. there's the Fluer de lys which is known to be the best. i think it's French food I'm not sure.
The area you should avoid is a neighborhood called Tenderloin. This is next to downtown and it's pretty noticable. The streets stink and the people look sketchy and you can come by some crazy people there. But the neighborhood is mostly harmless. The thing about downtown is the large number of homeless people hanging out in busy streets asking for change. Please don't give them change! They only keep asking and want more like $10. Sometimes they would use pets to get attention so try not to be fooled. Downtown has the top TOP name clothing brands and they're all worth a look but the prices are expensive! Union Square is basically a Square that you can sit and rest. There's free WiFi and there's a cafe. Also this si where you can purchase tickets and where you go to Tour buses on. Sometimes there will be events in this square so be sure to check it out if there's ever one occuring. The Macy's here is right infront of Union Square and there's a Cheesecake Factory on the top floor as well as a food court in the basement and even a post office. The Disney Store is popular place for kids, there's also a Saks Fifth Avenue, Neimus and Marcus (very expensive!), Levi's jeans, and more top names. There's alot of Jamba Juice and Starbucks stores in the city and if you never had them please try one of their drinks! If you follow down Powell St. to meet up with Market st., the main shopping area is right across the street. When you see a sign saying "Westfield" that's it. The mall has two sides, one side is newer and has the Century theater on the 5th floor. This is a huge shopping area so please do take a large part of your day looking here. Powell st. is home to a cable car line, but there's always a HUGE line at the ends, so the best way to get on is to wait at another stop. It's pricey to get on these things so get a tourist discount for these and the buses. On Powell, there's a Cold Stone which has very good ice cream if you never had them you should go and get some! Also on this street you may come by people handing free samples of stuff. If you're lucky you might get something for free. I've gotten food, energy drinks, and even a Quatro razor for free.
Grant St. has alot of top brand names so if you like high quality and expensive clothes, this area is really great. Right by here is the Fincial district where all the skyscrapers are. There are alot of great shops here, and the Crocker Gallery is worth a visit. There's a farmer's market there twice a week. Try the Soup Company and that one place that sell kabobs, both are really good! There's also great places to eat on New Mongomery st and 2nd st. The places in this area closes early and is especially quiet on Sundays. Market St. is a long street, so you can take the MUNI or the street car to travel up and down. There's tons of shops and places to eat. On Stockton there's the Apple store which is always popular, and across the street is 4th st, and you'll see the Metreon. This is a popular theatre and there's IMAX which cost $15 to see a movie there. They also got 3D too. There's an arcade inside and many places to eat on the first floor. For those who like comics and action figures, there's a store called "Things From Another World" that has really great stuff! Do check it out! Right by Metreon, there's a creme puff place called "Beard Papa" and its' very delicous! There's one in the mall but they don't have the large variety of flavors as the one here. On Mission street there's parking and places to eat that people wouldn't normally notice. There's a Mel's Diner, I don't suggest eating here because of bad service and food. Lori's is better but it's still not totally great. If you want to try Lori's, go to the one on Powell by EB Games and Walgreens since it's bigger and better food. Ok back to Mission st, there's a soft serve ice cream place that's also self serve. So it's self serve soft serve ice cream! Gosh that's sounds really odd. It's called Icebee, try this place out! Next door is a place called The Cravery which sells homemade pot pies that you can eat on the go. Their pies are delicious! They make and bake it in the morning and it's not microwaved at all! Totally healthy, lots of choices to choose from.
There are museums by the Meteron that are worth looking. MOMA is a great one to see! Oh yeah, the nightlife, it's very quiet late at night because everything closes early. Of course there's one little Walgreens that's open 24 hours and all year long, on Powell and sutter, and theaters will be playing till 1am. Clubs and bars have to close at 2am. There's two really good clubs and bars on Sutter, one is called "The Cellar" and the other right next to it called "Sugar Cafe." Alot of the bars are in alley ways or somewhere hidden in the buildings. At night, sushi bars are the usually the restaurants that are open. There's a great on that's underground on Taylor between Sutter and Post called Ryoko. Best sushi I've had so far. There's also Sushi Boat, Sanraku, and Sushi Rika that are pretty good.
ok, that's all I can say for now. I hope this was helpful! :)