The best thing I've learned is, if you're going out, never go out alone - you leave yourself vulnerable. If you've got someone else there you trust, they can say, be wary of that person. I probably used to be too trusting of people.
I think if you live in London, it's such a cosmopolitan city; nobody even notices different-race relationships. I assumed it would be even more liberal in the States, and it's totally the opposite.