It's all a matter of perspective.

Every time you take a picture, you get to choose your subject.  That's not usually a difficult decision.  Usually when we see a scene we like, we immediately know whether or not we want to photograph it.

But, what we don't always think about is FROM WHERE do we want to photograph it. Often, we photograph it from exactly where we first observed it. We bring the camera up to our eye, view the scene and press the shutter. 

I'll venture to guess that the vast majority of pictures most people take are taken horizontal, rather than vertical - it's a natural inclination as we seem to "see" horizontally.  I'll also guess that most pictures are taken from eye-level -- depending upon how tall you are, that's about an average of about 5 foot "something".

The question of "FROM WHERE" do we want to take a picture takes on several aspects. 

The following three pictures were all taken from exactly the same vantage point.  The bottom one was taken horizontally and the top two were taken vertically.  As you can see, the effects are very different.  Which one do you like best??  I happen to like the top-left image, but when viewing this thru the viewfinder, unless I made a conscious effort to analyze the scene and to try viewing it from different perspectives, I would never know which I liked better.

Experiment with different perspectives - they can make a world of difference in the pictures you take.