I'm as awkward and introverted as they come. If I can do it, I'm sure anyone can. It was only this past spring that I started (regularly) approaching strangers for their photos. I'm still refining my approach and I still get nervous, but I think I'm getting better at it. My general advice:
  • Smile.
  • Don't stalk potential subjects or linger in advance of approaching them. Best to look like you came out of nowhere.
  • Be confident and direct. "Pardon, would it be alright if I get a picture of you (and the boy/young lady/your family)?" That's my approach line almost verbatim.
  • Have a convincing response ready when asked, "What is this for?"
  • Context helps. Go to parks, parades, festivals, ball games, car shows, etc. They're great for this kind of work.
  • I'll second the notion that people who are ostentatiously (sharply or gaudily) dressed are usually more than willing to be photographed.

What follows, I won't call advice, but rather part of my m.o. This is what works for me personally:
  • I don't outwardly promise anyone anything about what I will or won't do with the photo. This is usually because it simply doesn't come up. That said, I'll certainly respect the wishes of anyone who asks. And I'm not dumping these to the internet anyway.
  • I carry business cards but hand them out only if people are interested -- or skeptical. I offer them a scan via e-mail and a print "if it works out." People typically don't follow up though.
  • I don't detain or engage my subjects beyond the business at hand. If they're interested, I'll chat for a moment. Otherwise it's, "That's great. Thanks so much!" And I move along.
  • I'm torn on the bit about the camera. I've taken lots of street portraits with my Olympus XA2. I travel light. That said, my confidence level increased, as did people's interest, when I lugged my Yashica Mat 124G to a local park recently.

The result? Most people (nine out of ten) say yes to me. In fact, what I'm finding, is that gaining access is the easy part. Composing a good portrait is the hard part.

At the risk of stepping on toes, something should probably be said about "profiling." Who you are and how you look (beyond "dressing nice") could have a lot to do with how people respond to you. People have their prejudices. Tattoos and piercings, for example, I think still put a lot of people off. So I can only speak for myself. I'm pretty featureless, for lack of a better word.