Download these two Photoshop actions here:

Darken Sky and Painterly Effects – Photoshop Actions

(This *.atn file needs to go into your Photoshop ‘actions’ folder [Photoshop Folder > Presets > Actions], and Photoshop needs to be restarted).

The first action allows you to put clouds into the sky. You will need to have a picture of some clouds to put there in the first place.

The second action creates a painterly effect with your image. Not watercolour, more like guache. Enjoy!