Subjects that portray a thematic contrast add interest and intrigue to a photograph. For instance, large subjects contrasted with small ones hold the viewer's interest as it’s necessary to study the comparison of items within. Contrasting colors, shapes, sizes, themes, etc., all have this effect. Using easily identifiable compositional elements to show scale is another technique to draw the viewer into your picture. Combining these tactics is very powerful.
In the image of the sand dunes, I used a tree to establish the grand scale of the dune. Without a reference point, the viewer wouldn't be able to appreciate the immensity of the sand formation. The grasses covering the foreground also act as a reference.
Look for ways to juxtapose contrasting subjects in your compositions. Also look for ways to show scale in your images. As you thumb through magazines, find pictures that depict these characteristics. Notice how these images tend to pop off the page. Study the compositions and apply the principles to your own photography. Contrasting concepts that work well are big and small, wide and thin, old and new, low and high contrast, vibrant and dull and any other pairing at opposite ends of the spectrum.