Thanks for the advice guys! I will be travelling in late April next year. Which are the mode of public transportation? I'm thinking if I should use the city bus tour or just go with their public transport.
Let's leave aside the open-top buses for now; those don't count as public transport, those count as tourist transport. Skip the cable-cars as well - they're like six bucks and they don't really go anywhere, they're a novelty at best.
Your main modes of transport are BART trains; Muni trams; Muni buses; the Muni streetcar; and Uber/Lyft.
BART trains go all over the bay area, and they're the main commuter mode of transit, so you'll want to avoid them during rush hour. BART's a great way to visit Berkeley (which you should do, Berkeley's great), or get from downtown to SFO or Oakland airport—it'll be about $8 per person, so if there's one or two of you it's way cheaper than an Uber— but it's not tremendously practical for getting around in the city because it only really runs along Market and Mission Streets. It's great for getting to El Farolito taqueria for a for-real Mission burrito, though; take BART to the 24th and Mission station, then pop up onto the street; El Farolito is on the east side of Mission, just north of the plaza. The burritos are brilliant.
Muni trams—the "Metro"—run underground along Market Street, out to the ballpark, and out into the suburbs. They're brilliant for getting out to Church and Castro stations in case you want to gay it up a bit, or if you want to go to Dolores Park and get an ice-cream from Bi-Rite Creamery because it's a nice sunny day, or if you want to go to AT&T Park to catch a Giants game (and you should, if you're in town between April and October!).
Muni buses: yeeaaaahhhh no. These work, but they're super slow; avoid them unless there's absolutely no other way to get somewhere (e.g. the Marina, the Cal Academy/De Young) and you don't want to pay for Uber.
Muni Streetcar: these charmingly retro streetcars run along Market Street, from the Castro to the Ferry Building, and from there to Fisherman's Wharf. They're wildly impractical because they're so slow, but they're a solid way to get from downtown to Fisherman's and back.
Uber/Lyft: if the regular public transport won't get you where you want to go, just use Uber or Lyft. It's cheap and omnipresent, and it'll get you to the weirdest corners of the city without having to wait for the creakingly slow buses.
Any good hotels and food to intro? Please leave down your notes.
Many thanks!
Hotels: I'm a Starwood buff, so I'd always recommend the Westin St. Francis or the Palace Hotel. Don't stay in Fishermans Wharf, it's miles from everywhere; stay around Union Square and catch the bus to Fishermans if you really want to see it.
Food: just use the Yelp app. Yelp knows all.
Most of the popular attractions are within walking distance of the city center. Do avoid the Tenderloin and the Downtown (CBD) areas at night though.
Downtown SF is fine at night, it's just a bit dead (though there's a few great restaurants around; make sure you get yourself over to Ramen Underground on Kearny if it's a cold night).
The Tenderloin can be a bit sketchy in parts, but I wouldn't totally block it off. Market Street is fine; if you like beer bars, Mikkeller Bar at Mason and Market is excellent, and the Golden Gate and Orpheum theatres, both on Market Street, are always showing something interesting. Even Sixth Street, which is unbelievably divey, has an excellent and dirt-cheap Vietnamese place (Tu Lan, between Market and Mission streets), and a brilliant wood-fired pizza place (Montesacro Pizza, down the Stevenson Street alley between Sixth and Seventh streets). Basically, there are homeless people around; they might ask you for money, but that's all they'll do.