Composing an image can be one of the most challenging aspects of any type of photography. What makes a good image?
Rule of thirds -
These lines can also be used to direct the viewer to one particular area of the image. Placing a horizon on the lower horizontal line with give more weight to the sky and thus draw the views eye to that area, like wise placing the horizon on the high horizontal line will give weight to the lower portion of the image.
But as with all rules, this one was made to be broken so play around and find your own comfort lines.
Lead lines -
More often these lines lead in from bottom to top, but again this is a rule and made to be broken, so play on.
In nature, plants are often a good source of symmetry, subjects with a strong reflection can offer a great opportunity for a good symmetry shot, placing the shore line central gives a balanced image of subject and reflection.