Remove unwanted levels

The levels in the picture are a fundamental concept, especially related to the portraits but which can also be applied to other types of photos.
The levels considered in photography are as follows:
General level. This plane is that usually incorporate a complete person, from head to toe.
The Middle short plane or flat bust. It is the map that shows the person on its upper half, creating greater attention on the subject, not the environment. It is usually up to the waist or chest.
Foreground. This is the map that focuses on the face of the model that we are photographing.
First Primerísimo level. Slightly more aggressive is that the previous one, closer still to the face, generally cut half of forehead to the Chin. Often complex control because we need to think in depth of field and the details and aberrations that can cause the short distance.
Level three quarters or American. This plane is basically the body of the model to the knees.
Photographic planes with examples
What you can do is modify an image, change the level. For example you've captured an image of whole body, but does not convince you, then you can work with a portion of the image, crenado a level three quarters or a foreground, for example.
The best is when you take the picture thinking at the level that we are going to choose that this is part of the composition, and depending on what level we want use we must think about the composition, the position which shall take the subjects, etc.
Other articles that can help you when working with levels in photography: