For a year I was too self-conscious to point a camera at a stranger. These are the steps that got me past it.
Photograph the light, not the person
Find a pool of light or a strong shadow and wait for someone to walk through it. You are photographing the scene; the person is part of it.
Shoot from behind and above
Backs, crowds and views from a bridge are full of life without anyone feeling watched.
When you do photograph a face
Smile, show the picture and ask if they mind. Most people say yes. If they say no, delete it in front of them.