Often we hear mention of 'leading lines'. Leading lines can be both imaginary and real lines in our photos that 'lead' the viewer to look at what we want them to look at. They use natural tendencies in humans to direct the viewer to what we think is the main point of interest in our photos.
Leading lines 'point' the viewer to a specific place in our photos. The below graphics show how lines in an image can make people look at a certain point.
Notice how your eyes naturally followed the lines to reach the point where they meet? I lead you to that point by 'directing' you to look where I wanted you to. Doing this in photography is going to help make your photography much more visually pleasing to the viewer. Now your lines in you photos do not have to be geometric (straight) they can have all sorts of shapes and curves, but what they must do is 'point' the viewer towards your main subject. So when taking photos, learn to look for lines and shapes that compliment and direct the eyes towards your main subject in your shot.
Here are some examples with overlays to give you an idea of what a leading line can look like in a real scene.
notice how all the lines here direct your eyes down the hallway, also notice how the 'ghostly' figure in the foreground breaks through those lines, this breaking of the line creates 'tension' and increases the effect of their being something 'not right' at that point. You can break your leading lines but do so for a reason.
The lines in this image lead you towards the officer's face, which is the subject here.
The lines do not all have to point to the same thing. There can be a primary and secondary main point of interest in your photos. Notice how the lines of the edges of the clouds point towards the brightest part of the sky, and how the lines of the waterline, the rocks and the waves point into the main area where the water is churning.
Learning how to 'see' and find leading lines is a great way to improve your photography. In a studio or posed situation, you can use a myriad of props to create these leading lines yourself. In nature, they appear everywhere. a fenceline, the waters edge, a dirt track, a jetty or wharf, footprints in the sand. Learn to 'see' them. Don't just turn up at a location and stick your camera down and shoot away, walk around, look for these lines.