One the most fundamental techniques necessary to really to master creative photography is depth of field. It was always a bit of a mystery to me because of the link to aperture and understanding all those back to front f-numbers. I think it was more of a mental block because it is actually quite easy to grasp.
Creatively you are able to do more with your photography and as you learn digital photography you will find using it key to great images. You can use it to blur out backgrounds while the subject remains pin sharp, or, create an image perfectly in focus from front to back as in great landscape photos. [read]