1. Gradient Fill. You can use a light and dark shade of blue, or like here, I used blue and pink to give it a sunset look.
2. Create a new layer. Switch back to default colors (black and white), and then select Filter> Render> Clouds.
3. With your cloud layer selected, change the 'Normal' to 'Screen' in the drop-down box in the Layers palette.
4. If you want, you can resize the image to give it a panoramic look. Image> Image Size> I doubled the width and left the height the same.
5. Erase most of the lower portion of the cloud layer.
6. Here I just used the Pencil tool with a dark brown shade to draw a rough outline of mountains
7. Use the Bucket Fill to fill in the mountains.
8. I added a couple of small details to the mountain.
9. Finally, to make the sun, Filter> Render> Lens Flare. Here I used the 50-300mm with 140% brightness.
Examples
