Poor composition is the most common mistake that people make when shooting vacation pictures.
But with a bit of practice, you can develop an eye for good composition and all of your photos will greatly improve. Then, align your points of interest along these lines. Notice how the points of interest generally fall along the lines of the grid. This is one of the simpler tricks, and is rather self-explanatory. Whenever possible, try to place main elements along an S-curve running through the frame from corner to opposite corner.