In this tutorial I will show you a very popular effect that gets a you a very cool lightning effect. The first thing you need to do is give your picture some texture. So go ahead and make a gradient.

Now go to filter> render> difference clouds

Now we are going to Adjust the levels to get rid of the unwanted clouds. So go to edit>adjust levels. And adjust them until you are satisfied, or use the settings below.

You should now have something like this:

Now just make a new layer, set the mode to "color" and fill it with the color you want your lightning to be. I chose purple.

And now your done! Hope you have fun with this!