Basically I just go up to people and ask them if I can take their photo. You've got to be nice about it, and have fun with them to make them relaxed. I explain its either for a book I'm working on or this website. Generally just be nice to them. The people I photograph have usually caught my eye for some reason so I tell them why. If some random person looks cool, I say so. If a girl looks stunning, I say so. If a couple look like a cute couple I say so.