Choose a suitable photo depending on how many lights you want to turn off, how many light trails you want to clone out, how much detail you want in your daytime sky, etc. If you get something with a dark blue tint at night, its easier to brighten it into a lighter blue.

Five layers of screening, One layer of the merged result which still had stars in it. I selected the sky, placed a copy of it on a new layer and blurred it till the stars were no longer visible. Made another copy of it and played with hue, saturation and lightness till it was less purple looking. Duplicated it again and decided to add another 50% screening.
Took a copy of the merged foreground and decided it was far too light due to all the screening so I duplicated it again and blended it on 50% multiply.
Played around with color adjustments hue saturation, contrast, cloned out lights on the background hills and merged all layers together.