There is an easy answer…. Do not put it dead centre of the photo otherwise it will look like a snap shot. So where should you put it?
First of all decide what part of the image you wish to emphasis – the sea or the sky. If you have a great looking sky then put the horizon at the bottom third of your photo. This will lead the eye to the most interesting part of the photo. If the ground is more interesting then simply do the opposite, put it at the top third.
Can I break this rule? Of course! Rules are to be broken….
If you are shooting a landscape shot with a boring sky try eliminating as much of it as possible. Make it 7/8 ground and 1/8 sky, so the attention is off the sky and totally onto the more interesting foreground subject.