Then, grab the Eraser Tool and select some quality line brushes from you’re Brushes.
(if you don’t have any, you can download the same set: HERE)

Use the Eraser Tool on low opacity such as: 40%.

And here’s the result.

For the end you might wanna try to merge everything and add some Lightning Effects on it, such as: Omni Light in example.

That’s it, you’re done. Congratulations!