I have tried my hand at some of these recently and it has been fun as well as a learning experience. If painting in the studio I look through my "art ideas" photo file and edit by cropping them different ways to see what might work. Basically I look for a better composition within the image.
Photo of a beach on Cape Cod- what interested me most was the horizontal arrangement of the colorful umbrellas. The foreground didn't add much.
And from this the painting on a 6"x12" panel-
Next a photo of waves on our local beach- I love the energy and movement of the waves breaking from the center to the right in the upper half of the photo.
And the painting on a 6"x12" panel-
As for vertical formats, I have not tried this with a landscape other than tree portraits which easily fit. Here is a plein air example, 10"x8"-
For an even more vertical format I tried a cat portrait 16"x8"- I think his tail makes it all work-
Obviously I cropped the original photo quite a bit.
Try looking at your photos that you like but have yet to inspire a painting. They might work well in a different format.
Thanks for reading!