All photos taken contain lines, some there intentionally and some put there subconsciously. Vertical lines create height, they are usually found on buildings, trees, fences etc. horizontal lines can sometimes represent calmness and peace. They can be found on dessert, lake, field and many other images. Diagonal lines give a motion feel, for example trees blowing in a strong wind, a running person, a mountain or slope. Curve lines are mainly found on bodies but can also be found in many places including rivers or pathways. I particularly like leading lines, they lead your eyes into the pictures easily. Successful leading lines take the eye right to the main subject or focal point in an image. With composition in some cases symmetry can be a key element. Symmetry in a long shot using leading lines can create a striking image. Using the rule if thirds can also help a lot, making sure there are no big empty spaces and there is a focal point creates good composition. The image below displays several horizontal, vertical and leading lines, all supplying different effects.
The image below shows many lines.
The image below shows good composition and also symmetry, the picture was taken exactly in the middle of the bridge which is why there is symmetry however only on the bridge not in the background.