Use triangles to emphasis a subject. The idea is to put the primary objects inside a triangle or we could put the primary objects outside of the triangle. We can even use multiple triangles.
An image can have several triangles
Leading lines pull the eye into, or out of, a scene
Here the road acts as a leading line to draw us into the image.
The slope leads the eye uphill (or downhill depending on how your brain works). In this case, the slope pulls the eye which makes it more likely that the viewer will see all of the elements in the scene, not just the obvious one.
Here the train and tracks lead the eye into the background of the image.