1. London is the most diverse place I’ve ever visited. It’s hard for me to imagine anyone not blending into the crowd, there.
2. Hostels generally have places to lock up your stuff and it’s really only a small part of your stuff that’s a target for thieves. No one wants your back pack full of dirty laundry. Cash is the biggest target. ATM and Credit cards and anything small, valuable and easily portable are other targets — although your expensive camera is probably only worth a few bucks to a thief. Use a money belt. Minimize small electronic stuff like Ipod, camera, phone, etc. and keep that stuff with your or locked up. Do not flash large amounts of cash or fancy electronics.
3. From the standpoint of personal safety, you’re probably much safer in UK than you are at home (depending on where “home” is). Use common sense. Avoid places, especially after dark, that seem deserted or somehow “wrong.” You might attract some unwanted attention in UK, but I think it’s unlikely. If you do 1) Ignore. If that doesn’t work 2) firmly say “go away” or “leave me alone.” 3) If all else fails make enough noise to attract attention. IMO, there’s a tiny difference in perception from the US. Direct eye contact, a big smile and “hi” to a total stranger on a US college campus isn’t out of the norm. It is slightly more likely to be interpreted as a come-on in Europe. Sunglasses can help avoid unwanted eye contact.
4. Keep track of your stuff, especially when you’re likely to be distracted (taking a photo, browsing guidebook, buying souvenirs) Act like you know where you’re going. If you need to consult a map, pop into a store or cafe.
5. The packing forum will help with what to bring. The two basic rules of packing are:
a) 1/2 the stuff and twice the money
b) Tickets, plastic (ATM and credit card), passport: you can buy everything else after you get there.