Personally I don’t do much asking because I want to capture something as natural as possible. Street portraiture is fine but I don’t really shoot with the proper gear to make my subjects look as good as they should.
I understand the desire to capture people as authentically and naturally as possible. My favorite kind of photography is candids of people, who are either unaware I'm photographing them, or they just don't care. When I started shooting people on the street, I always shot in stealth mode, because I didn't want them to pose. I don't like posing people.
Another part of the equation, for me, is that I'm uncomfortable and nervous about asking people I don't know if it's okay to photograph them. It's entirely possible they'll reject my proposal, and they might be annoyed or think I'm some kind of weirdo. That's another part of the reason I shot mostly candids of people on the street: I didn't have to interact with them.
But over time, I became increasingly aware that I was violating their privacy. And I decided to stretch my own boundaries, push the envelope, so to speak, by approaching people. There are scenarios where people are doing something that is interesting or fascinating, and if I approach them, I'll destroy the authenticity or spontaneity of their behavior. In that case, I might still shoot a candid. But now, 90% of the time, when I spot something interesting in a person's appearance or behavior or energy, I'll approach them and engage. I explain, briefly, why I want to shoot a photo of them, and I can usually find something flattering to say about what I'm observing, such as, you have an interesting/cool/unique look, or energy, and I'd like to photograph you, if that's okay.
I'm always nervous when I solicit a street portrait, but I've met some interesting people using this approach, and, more often than not, they seem pleased that I took an interest. Most of the time, I ask them if it's okay to share their picture in a public forum, like Flickr, or Instagram, and they want to see the image after I post it. I have a business card I give them that has links to my website and Instagram, and they can look me up on Flickr, if they're so inclined.
Flickr has a group called "100 Strangers," where you approach a stranger on the street, have an interaction with them, photograph them, and post the image, along with a description of your interaction, in the group. I got into this for awhile, and I've used the same format on my blog. It's both scary and fun, and again, I've met some interesting people and heard interesting stories.
Here's a link to my 100 Strangers album on Flickr.
And
here's a link to my Instagram account.