Leading lines and the s curve can be used to bring depth and movement to you picture drawing people in. With strategic use of lines whether as a curve or perspective lines you help lead the viewers eye into your photograph and create different moods. Below are a couple of examples of how this principle can be used. The S Curve – used to emphasise / create depth

Leading Lines – used to show speed / to lead your eye to subject

I have to confess I don’t find myself consciously looking to use the s curve a lot and am going to have to remind and challenge myself to find opportunities to use them.  I naturally tend towards some of the other composition principles like perspective lines and framing.

Other Post on Composition
Simplify Your Subject
Rule of Thirds
Composition Printable
Beware of Mergers
Symmetry & Balance
Cropping