Let me convey some advice as a guy from Slovenia (EU) who just went through such a trip last October. You are also required to buy me a cup of tea somewhere in the next few weeks when I'm done with exams :P
Here are some random notes in no particular order.
1. Decide what you're going there for, just doing a general soul search and so on can get pretty wasteful. Have events/conferences lined up, if you can also have meetings with interesting people lined up. A fortnight blazes away sooper fast if you don't know what you're doing!
2. Go see the Golden Gate Bridge, I didn't, it still feels weird telling people I was to SF and didn't see it.
3. Alcatraz is over-rated.
4. I can get you contacts with a guy that might be willing to get you a tour of Apple. He's a friend of a friend and works there. You won't be able to see much more than the restaurant and backyard. They're hellishly secretive.
5. Google is a bit less secretive, but you need to find someone who will give you a tour. I was lucky enough to get in with the Startup School tour last year.
6. A lot of everything seems to happen in Palo Alto, so perhaps try staying somewhere close by. You should definitely check out University Street, it's pretty nice.
7. Cheesecake Factory is not just a thing from The Big Bang Theory, it exists and the cheesecake is absolutely delicious. (university street Palo Alto)
8. Five starbucks checkins get you a free coffee.
9. There are only two starbucks open after midnight in the whole general area.
10. Use yelp and foursquare to find good places to eat. Foodspotting might be a good choice.
11. Do visit San Francisco, Mission is pretty cool because that's where the hipster/startup scene is. Go visit the mom&pop coffee shops to get a blast from the past and an awesome experience of how homely something can be (also awesome places to work from)
12. Don't buy the large Cola if you go to the cinema. It's something like a liter of cola.
13. If you're into that sort of thing, there's a lot of cool culture to be seen in Mission, Victoria theatre seemed awesome.
14. Don't forget to go partying at Ruby Skye one night. You can get in for free if you sign up via the internet a day before. It's the club where Zuckerberk meets Timberlake in the movie.
15. Everywhere you will eat the portions will be way too large, everything other than fast food can get pretty expensive. You will likely eat meat at least twice a day, try to avoid this, I nearly died ... but it's hard to find somewhere that doesn't serve primarily meat (or maybe I'm just very silly in finding places to eat)
16. For a cool shopping experience visit the huge mall in SF financial district, it's about the size of the downtown area of Ljubljana.
17. We mostly stayed in motels, they're very cheap and they all mostly have wi-fi. I think we ended up spending something like $20 per person per night.
18. The weather is very warm, but you will acclimatise quickly and start feeling cold at anything below 20C.
19. Remember that this is the US. Everything is very far away. Plan accordingly. If you're savvy enough I'm told it's possible to get super cheap rent-a-car at the airport. Think we ended up paying something silly like $20 per day for the car.
20. Visit Dog Patch Labs at Peer 13, it's an extremely pretty incubator and overall awesome.
21. There is a nearby chocolate startup, we didn't visit, but I'm told they hand out free chocolate.
22. Fly with Lufthansa, it's cheap and sufficiently comfortable.
Ok I can't think of anything more, if you buy me tea I might come up with more little tips I picked up along the way.
PS: don't get lulled into spending too much money. Everything is at a roughly 40% discount in regards to the Euro and it can get you spending really really quickly.
PPS: http://meetup.com, go find meetups.