Rule of Thirds
One of the most common rules in composition is the rule of thirds. Basically, if you have a line, you move it to be one-third in from the edge. On the image the below, the 1/3 lines are dashed. The circles represent where the lines cross, being an extra strong spot to put a focal point. (Not four focal points, just one. But there are four strong places to try one out.)
Notice how in the painting, the rock in front of the setting sun is located where one of those circles would be in the composition. Avoid putting the focal point right in the middle of the page.
It can be common to have a photo taken at a tilt in comparison to the horizon. And, then to accidentally copy the tilt. Make sure if you have the horizon of the ocean, that it is straight, not crooked.
It is easy to be distracted by the ocean itself. But is your composition going to be interesting? In the painting below, the composition may seem simple, but has lots going on in the foreground. The sky is reflected in the pools in the sand. There are lots of leading lines created by these that go up towards the ocean.
Take a look at your composition before you start. Would it be better if it was cropped? Where does your eye go? Is your main focal point in the middle?