I'm from London and I got back from SF in November after doing a month long trip there with my co-founder. We went because we fell that London just doesn't have the same vibe and opportunity so we set off to meet like-minded people, investors and to work on our product.
One thing I highly recommend is entering hackdays, we ended up winning one and not only came away with a small cash prize (some have huge prizes) but also agreed investment in the idea (which is completely unreleased to our product. This opened up opportunities like you wouldn't believe. It was a nice break from building our thing too.
In one month we made inroads to investors and were very close on meeting some great ones but our time ran out, if we had another month im sure we would have got some face time with one or two guys but they are extremely busy. We used meetup.com and eventbrite to find out about events such as a talk by the Yammer founder on starting up and getting acquired. I also noticed that some fanastic talks happen that aren't on those sites, like ones at AirBNB and Asana. I saw a amazing talk by a guy who helped set up the tech behind Reddit, even as a designer I thought it was fascinating how they scaled.
Sign up to the Startup digest which collects all the events in SF each week and emails them to you, really great http://startupdigest.com/
I'm sure you know this already but it's all about making connections to people and getting recommended. If you are passionate about what you do and show that through your work and conversations then its easy to get endorsed by people. I found that the process is gradual, you meet someone who knows someone who knows someone, getting time for a coffee with people may take a hour or 2 weeks.
Beware of time wasters. It's easy to find yourself at events and in meetings that have no benefit to you. I went to a lot of things expecting knowledge sharing only to find that I was trying to be pitched to or hired. There's a lot of people in SF on the startup wagon looking for designers and developers to work on their idea with nothing more to offer than equity. Pick and choose events wisely.
We stayed on Fell Street, near Alamo park in a apartment found on Airbnb. It was a nice and safe area, the accommodation was pricey, roughly £2300 for a simple, smallish 1 bedroom apartment (we took turns on the sofabed futon thing).
Mexican food is everywhere and it's amazing. In the same way London has kebab shops, SF has Taquerias and they are super cheap $6-9 for a burrito stuffed with meat. I don't recall having one bad meal in SF.
I you could learn more in SF in 6 months than you could in London in 2 years. The place is buzzing with activity, there's literally something brilliant going on each day, whether it's a hackday, founder talk or meetup. Add that to all the non-startup stuff going on like food festivals, street markets, Alcatraz and its great.