Leading lines make the image “more powerful”. They should lead the eye to a certain point (or object, or part of the image) that you want to put “into the middle of your image” (even it’s not the geometric middle. Lines are helping to create a mood in an image as well, they become even more powerful when they are also used to direct the viewer’s attention.
Horizontal Lines
They tend to create a resting picture in balance, they produce stability and evenness. It’s the opposite of dynamics in an image.
Vertical lines
Vertical lines can project either a mood of stability or peace.
Diagonal lines
They can convey a sense of action or make an image more dynamic. From left bottom to right up they often produce a positive feeling, while vice versa the effect produces a more pessimistic mood.
Intersection of lines
They lead the eye directly to the intersection point.