>>41235891st way to gor about it:
Find a good spot, set up your shot, wait for someone to go in. Since you were there before they walked in they usually won't think that you took a picture of them and quickly walk out of the frame.
2nd way:
Waist shots or sneaky phone shots. When no one is looking set up your camera/hand so that you're more or less level and know how much is gonna be in the frame. Then just fire the shutter without looking at the camera (or your subject).
3rd way:
Zone focus and pre-expose, take a quick shot (works better if you already have your camera in hand and up to your chest, as it minimizes noticeable movement), then keep walking and look behind them.
If they somehow notice or suspect something, the number one thing is to own up to it. Smile, say something witty, thank them and say they looked interessting. Confidence is important, don't be a creep taking creep shots of people. Be a photographer taking photos of beautiful people in public, then you have nothing to hide. You have to work up this confidence.
The chad way to do this is be conspicuous and take your shot and look at them right in the eyes. If they smile back and show no discomfort at getting their photo taken then you can get a couple extra shots. More than that will probably seem creepy and paparazzi like.
Also something worth keeping in mind in all situations - learn to read people, know your environment and don't try anything if someone looks shady or not in the mood to be photographed.
