This is my second time in SF, and it’s an awesome place. In the spirit of helping others to get the most from the city, here are my tips:

• Read up beforehand. I recommend the book, “San Francisco Bizarro”, and the LaughingSquid.com blog. BoingBoing.net also covers some cool things in the Bay Area as well. Upcoming.yahoo.com has a great list of events, and there are several street press magazines you can read once you arrive.
• Public transport is pretty good. The BART is an excellent means for getting from SFO to your accomodation, and the Muni has been fine for getting around places not near the BART.
• Accommodations can be pretty expensive, but if you know where to look they can also be pretty cheap. I found a good place through AirBnB.com, and some hotel rooms through google searches. The Taylor Hotel (615 Taylor Street) is two blocks away from Union Square but only $60 per night (about $70 with taxes included). It isn’t luxurious, but it is central and it’s a third of the rate at the Marriott I stayed in during WWDC. I’ve also stayed in the Pacific Winds backpacker hostel. It was good and the people were fun, but you don’t get any personal or private space. I find I can cope with this fine for a week or so, but then need a couple of days where I have my own private space to chill out in. After that I can happily return to shared accommodation. Try not to be in denial about your needs for personal space, even if it’s only for a couple of days — it will be a lot less stressful for you and the people around you!
• Be aware of your surroundings. The Tenderloin is an area in central San Francisco that is just off Market St, and I have been repeatedly warned that it gets dangerous after dark. The cheapest hotels in the city centre tend to be on the edge of the Tenderloin, and will be safer to approach from one direction than another.
• Usual traveller rules apply: don’t make yourself an obvious target. Talk to other travellers and the reception staff at the hotel. Don’t keep all your valuables in one place: I have money and a credit card in my wallet, in my backpack and in my laptop bag.
• San Francisco has mild winters and some decent free health clinics, so there’s a significant number of homeless people around. I haven’t seen any of them do anything beyond begging or sleeping in the street, but it is pretty full-on at times. Yesterday in Union Square (Taking photos of Macy’s, Tiffany’s and Victoria’s Secret massive flagship stores) I watched a guy who might have been 18 searching a bin for leftover food. Some of them smell really offensive. Some have mental disorders. Keep your cool and keep walking — unless you really want to spend some time talking to them or you want to give them some money. But decide ahead of time how you will deal with them, because you are in for a pretty upsetting time otherwise.
• Tipping. I think this is a pretty bullshit way to organise things, but it isn’t my country. The minimum wage is so low here that service staff need tips to cover their rent and food expenses. Not tipping or giving a low tip (less than about 15%) is seen as an insult to the service. This leads to all kinds of predatory behaviour, especially in more expensive restaurants. If they can convince you to get a dessert and a coffee for $13, that’s an extra $2 on their tip. Prepare for some very friendly behaviour followed by a lot of upselling on drinks and desserts.
• Coffee. I like the Italian-style coffee in Australia (Cibo, Lavazza, Illy, etc…) and the regular American taste is way too bitter. It has been explained to me that they assume you will have a lot of sugar or a syrup shot, as well as cream or milk, so they blend and brew a more bitter coffee to balance the flavours. Go to Caffe Trieste in North Beach or Blue Bottle Cafe in SOMA for (in my opinion) an enjoyable coffee. They will both have lineups continuously, so be prepared to wait for a few minutes to get served. I find that Starbucks can be great if you go in there looking for an adult milkshake!

Most of all, make friends with the locals! SF seems to be the collection point for the smartest, most creative and curious people in the western parts of the US, and if you are open to it you can discover some amazingly cool people very quickly. It isn’t all about Silicon Valley either, there is a lot more culturally active stuff to engage with than you would think. SFMOMA and the Exploratorium need to be experienced, at the very least, and I highly recommend doing the bike ride from Fisherman’s Wharf across the Golden Gate Bridge on a sunny day!