Before you start to work, it’s best to decide where your horizon is, portrait or landscape.
Composing a picture, A, B, C, or D are where the center of interest should be, then compose the picture around it.
Examples of positioning your center of interest. Don’t put your horizon line in the middle as it cuts your painting in half. You can have a horizon anywhere, but try to avoid the middle.
If you have a wide view, the best way to find a good composition is by using a viewfinder, which you can make out of card.