Take a look at this photo.
Well the horizon line about halfway through the photo doesn't help, but the only subject is the African plain which consists of acres of grass and a few bushes. Although there is a herd of animals in the far distance, it is difficult to see what they are. There is no real point of interest. The eye scans the photo, finds nothing to focus upon and you get bored very quickly.
Now look at this photo which is similar but has a subject.
So from these examples we can see that there are a couple of important factors regarding Subject.
1. The subject should be OBVIOUS. It is the centre of interest to the viewer.
2. The SIZE of the subject is important to the viewer.
3. The POSITION of the subject is important. (See Tips - Rule of Thirds)
Even with cropping, the photo isn't great because magnifying the image introduces noise. But it is better than the original because the subject is larger, is better positioned in the frame and these is some foreground interest which also provides environmental interest.
The temptation of many photographers is to photograph what they see. However, depending on lens choice, the camera rarely sees a scene how the human eye sees it. This is particularly true with landscape photos. The eye scans the scene as your head moves to take in the whole scene. Therefore we see a composite view while the photo is a single frame. The result is often disappointing.
So choose the important part of the scene and concentrate on how to show it at it's best.
SELECT then COMPOSE.