Step one:
On a new layer, create a black to white gradient, diagonally from the top left, to the bottom right.

Step two:
Filters>Render>Differance Clouds

Step three:
Now invert the image. Cmd/Ctrl+I. You can start to see the lightning

Step four:
Adjust levels to bring out the lightning, Cmd/Ctrl+L. In the levels box: slide the black arrow to the right and the middle one to the right too, until it looks nice and clean

Step five:
Now to add a bit of color: Go to Hue/Saturation Cmd/Ctrl+U Click the colorize box and slide the Hue till you like the color."

Step six:
Now to add it to your image: Just place the lightning on a layer above your image and change the layer blending mode to "screen". Here I duplicated the lightning layer 2x and rotated it a little.