This youtube video is a good start I reckon, finding good scenes is a big part of it. Waiting in a spot for an appropriate thing is better, the people around see you with a camera and have time to be more comfortable or get used to you being there.
Many people allow themselves to be freaked out or influenced by media stories, so there will be the odd person that complains, simply delete the image, basically they are insecure, but most people won't mind, that is how I see it here.
Getting back to the youtube for ideas. As there are too many, just, shots of the street with people in it. What makes it interesting is the job for the photographer. Maybe have a certain story to tell eg. Bill Cunningham wanted to tell the story of fashion on the streets. When you have a mission it is easier to tell people what you are doing, if they ask, than if someone is just doing random shots of people, as such, with no story.
Discreet camera is better.