One of the most important things to learn in Photoshop is how to replace the sky. This is crucial for landscape photography, but it is also very important for other aspects of photography as well: travel, architecture, portraits, and wildlife, for example. In this picture, I hired a dance company to dance and pose for my photo tour group in Indonesia, and i specifically chose a time of day when the light was soft and diffused. However, the sky turned out white. So, I replaced it with gray clouds that matched the lighting on the scene. That made a huge difference.
I am writing a new online course called 'Post-processing', and it will be available within 10 days from now. One of the lessons explains how to replace the sky in various situations so it looks completely believable.
I took this setup shot with a 15mm fisheye at 1/50th of a second, f/3.5, and 400 ISO. I hand held the camera.