Can you see shapes? I'm going to date myself and say remember the old toy Colorforms. Photography is Colorforms. Can you see the vertical and horizontal forms and figures in a scene? Learning to see shapes will help you dramatically with composition and give you the answer if your image should be vertical or horizontal. In this black and white picture of the Huntington Beach Pier, I went with horizontal view. When shooting landscapes of the beach, the horizon will most likely force to keep the camera horizontal. Seeing shapes in photography is not automatic; if you stick with it like the Colorforms, it will become a habit. So get out there and shoot some shapes.