When you first look at the picture below, think about what your eyes do. Mine follow the line of rocks from left to right every time. They make a pathway through the picture, and our eyes are drawn to it. We circle back around and look at the whole, but the first reaction is to follow the line.
They can go from bottom to top
or top to bottom.
Think about it when taking pictures. Add in an element that will lead the eye where you want it to go. Handrails and fences are great for that, but any line can do the job. Notice the railing on the bus in the picture below. It leads the eye up the street, so do the lines on the pavement, so does the line of cars (even their direction), so do the walls of the buildings (especially the horizontal lines like on the Home Depot). Don't your eyes want to go right up the street?