1. Take your camera everywhere. Carrying your camera everywhere allows you to be able to take a picture at any moment. The people around you may also become more comfortable if you always have a camera because they start to expect it from you, and then they are more relaxed when you start taking photos.
2. Use a long zoom to allow yourself to get up close pictures of your subject without being in their personal space.
3. Do not use flash when possible because it will let people know you are taking pictures, and the harsh flash can ruin your candid moment. If you're in low lighting increase your ISO setting, use a faster lens, open up your aperture or use a 'natural light mode'.
4. Shoot from the hip so your subject does no see you raise your camera to your eye and become tense. It may help to set your lens to a wider angle setting to makeup for aiming problems you may have.
5. Frame images by purposely including foreground elements to make it look as if you're hiding behind it.
6. Try new perspectives and break the rules of composition to get fresh and surprising photos.
7. Photograph people doing things. Wait until your subject is completely distracted by whatever they are doing, then start taking photos of them.
8. Photograph people with people, because even if they are not interacting it will show a relationship and add more to the story.