Refining the background
I add clouds in the distance to push the scale even more and add colour variation to complement the ship. I also tie everything together with an overall colour adjustment. For this I use Adjustment Layer> Gradient Map set to Soft Light and on a low Opacity. Gradient Map layers are a great way to tweak colour because they affect the whole picture based on its value structure.
This vehicle looks too new: I want it to look like it’s seen some action. So I duplicate the ship’s layer and lighten it with Adjustments>Levels. Then I apply a layer mask to it and invert the layer mask so the layer becomes invisible. Now I can paint small scratches with a painting brush. This is a step where you can experiment and have fun, so take your time.