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




2. Filters>Render>Differance Clouds




3. Now invert the image. Ctrl+I

You can start to see the lightning




4. Adjust levels to bring out the lightning, 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




5. Now to add a bit of color:

Go to Hue/Saturation Ctrl+U Click the colorize box and slide the Hue till you like the color.





Hope this tutorial came in handy.