Extract With channels
I often use channels to extract out sky and other elements, preferring it to the Magic Wand Tool and the like. There is a lot more control in painting in the sections needed by using the Color Dodge and Burn tool after copying the channel that has the most contrast for the element that needs to be extracted. I also use tool presets such as soft brushes set to Color Dodge or Burn if I need more harsh painting. This is because the Color Dodge/ Burn tools have their own automatic ranges of Highlights, Midtones and Shadows that you must select before painting, but I personally prefer being able to paint with the Wacom pressure sensitivity. Once I have a mask that I am satisfied with, Ctrl-clicking on the thumbnail of the channel loads up the selection that can then be used to create an automatic mask.