Some of you may well know what cropping is, but many of you may not know where to crop for the best or why we crop at all.

Cropping is what we do when we want to emphasise the subject in our photos. By cropping, we can also alter the balance of the image. For example, if our subject is bang in the centre of the frame, by cropping, we can alter the position of the subject with the frame. But why go to all that bother? Why can’t we just leave the subject where it is? Alright, alright, for an explanation of that, check out my:
"Rule of Thirds Explained".

Cropping is also handy for taking out any little nasties or intrusions that we don’t want to include in our photos.
But let’s go back to the beginning and I mean right back to even before we actually take the photos in the first place.
Before you raise your camera, give yourself a second or two to assess the scene and you really should ask yourself these important questions:
1) How close can I get to my subject?
2) What is the background like? Are there any bright areas? Anything that
does not relate to my subject. Can I alter my viewpoint or change to a
better angle to eliminate those things?
3) Can I get in even closer still? What about if I turn the camera on its
side and take the shot that way.
4) I’ll use the zoom to its full extent, then I will get only what I want in the
frame and very little else.
There are many other things you need to ask yourself when you compose your shots, but here, we are only concerned with cropping.
So, now you can really understand what cropping is. It is a matter of eliminating that what you don’t want in your photograph and getting closer to your subject. And all that should be done in your mind as a sort of pre-visualisation, before you actually press the shutter button. This will not only help you become a better photographer, but it will save all that extra time working on your photos when you eventually get them all up on your computer later.
There will of course be times when you want to include part of the background with your subject, but at least be aware of what is being included. Because the things you miss, your camera will only pick up.
If you would like to extend your knowledge of this subject, might I suggest you take a look at my: “Composition Design” chapters 1-7 and don't forget to have a look at: “Rule of Thirds explained”.

See also "Amputation"