How to create lightning bolts

Step 1:

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

Step 2:

Select Filters>Render>Differance Clouds

Step 3:

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

Step 4:

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 5:

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.

Result:

Step 6:

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.