You have no doubt heard the term lead-in lines – which are lines that direct the eye where you want it to go. This is a powerful tool in composition and can add a three-dimensional feel to your image. It does this by creating movement and can take away that static/flat feeling.
Lines can be literal (such as roads, streams, power lines, or fences) or implied (those that link different subjects in the frame). While diagonal lines are considered the strongest, you are not limited to it as experimenting with horizontal, vertical and converging lines can also be a source of inspiration.