I sometimes look to the photographers knowledge bank: rule of thirds, lead in lines, especially for landscapes as it is a good way of creating an aesthetically pleasing image. Final cropping can help to remove unwanted or distracting elements, and of course retouching, this depends on the shot but should be done with care.
For this landscape shot in Dungeness, the portrait format emphasised the tracks which create a lead in line towards the delapidated shed and horizon which is towards the top third of the image. Also notice that the shed is in its own space, If I had moved to the left or right, then the hut to the left and boat to the right would have interfered with the clean lines.