Take a photograph that must include the waters edge and something or someone at the waters edge.  Try to make it that this something or someone is the focal point of the image.
Make it a photo that is “framed” and ensure no unwanted or distracting elements (such as a stray telephone or power cable).
The waters edge can be anywhere that is the edge of a stretch of water: sea shore, bottom of a sea cliff, river bank, lakeside, or even a puddle.
The something or someone might be a water bird, an animal, a surf-boarder, a child paddling, driftwood.  Let your imagination fly!