Compostion refers to the arrangement of the artistic parts so as to form a unified whole. In addition to the quality of light and color, arrangement of the subject matter is the heart of photographic composition. The primary technique used to achive good subject matter arrangement is the "rule of thirds".
The rule of thirds primarily refers to the division of an image into 9 segments. For any image two equally spaced horizontal lines, and two equally spaced vertical lines can be drawn. These lines can be used as guides to add interest to your photograph.
Use the lines to align either the horizontal and the vertical lines of your image or to divide the image into regions for your subject matter. In the example above, the handrail is on a horizontal line. The young woman and the waterfall are located approximately in opposite vertical thirds of the image. You can also use the intersection of the lines to highlight any particular part of your image.
You'll also find the term "rule of thirds" referring to the depth of an image. In most photographs the greatest attention is paid to what is called the foreground - this is the face in a portrait, or the background - this is what is seen in the distance. There is also, however, a middleground and in vacation photographs adding interest here can improve your composition.
In the second example, the young man is in the foreground. He is certainly the subject of the photograph. You can also see he is in an outdoor setting as is shown by the trees in the background, but it is the middleground that tells a bit more of his story. Why is he sitting on the huge rock? It's probably not in his back yard, so how did he reach it? His posture and expression indicates he's resting, so it must have been a challenge to get there. Conclusion: He's on an adventure, and the image has captured an achievement along his way.
When taking vacation photographs look around you. Be aware of the contents of your composition beyond just the subject of your shot. Give attention to the "other things" you see in your view finder. You'll be surprised at how much more interesting your photographs become.