First, I try to pay attention as to where the focus of my camera falls in a picture plan and how deep it is. Second, I always choose my exposition very carefully so as to neither underlighten nor overlighten an image. And third - I do many, many tries. You see about the tenth part of the taken pictures. Most of them go straight into trash.
There are some other fine points, but those three are the most important.

PS: Oh, and you want to have at least a good camera, if not excellent. With some good optics, that is to say - with nice, BIG aperture and reasonable light-grasp. You can't take good photos with poor camera, you really can't.