On photographing strangers
People always ask how photographers go about asking total strangers for permission to make photographs of them. It’s really pretty simple: Just be friendly and polite, that’s all.
Talk to them a little before asking. This will help break the ice and help them to relax. When you ask, compliment them on their appearance - something along the lines of “you look really great today - I’d love to make a couple of photographs of you. Would that be okay?” Be sincere, don’t just make crap up. People will know when you are just patronizing them to get what you want.
If they ask what you want to do with the photos, be honest with them. If you might enter their photo in a contest or exhibit it, tell them so. If you are shooting just to hone your skills, tell them that, too.
Give them your card with your contact information (you do have a card, right??) and offer to email them a copy of the photo after you have processed it, and be sure to follow through on that if they email you and ask for a copy.
Being friendly and sincere with your prospective subjects goes a long way.