I'm a street-shooter at heart. To do it well, one of the most important skills I had to learn was how to minimize the lag between seeing a great photo and taking it. We can debate the ethics of photographing people without their prior permission some other time. For now, let's just assume that you're taking candid photos of friends and family and that you want to capture spontaneous moments that don't look stiff and posed.
You might think that today's fully automatic, point and shoot digital cameras would be perfect for this sort of thing, but they're often too slow and too automatic for the control you need. Even a DSLR isn't much better if you depend on the camera to do your thinking for you. You'll get much better results if you take care of every important setting before you raise the camera to your eye. That way, you don't have to focus, adjust exposure, ISO, light balance, direct, or anything else. You just frame and shoot.
This approach obviously works a lot better if you're using an adjustable camera. Fully automatic cameras tend to "fight back" (strictly in the interest of protecting you against yourself, of course). In any case, preset as many parameters as you can, with a bias toward a fast shutter speed (to freeze action and camera shake), a small aperture (for more depth-of-field), and a medium focusing distance (to fall within the range of sharp focus). Increase the ISO if necessary to get an exposure that falls within the range of 1/500 second at f11 or 1/250 at f/16.
Then just wait, with your camera in your hand, resting at your side, and your finger on the shutter button. When you see what it is you've been waiting for--or something better--raise the camera to your eye and gently release the shutter. No doubt, no hesitation. Once the moment has passed, drop the camera back down to your side. You don't want to make a spectacle of yourself or the person you're photographing.
If your subject notices you, smile. Why not? The two of you just shared a moment together. The more you do to keep ego and equipment out of the way, the better that moment will be.

