Another special effect that you may need for your illustrations is lightning or electricity. The results look difficult to achieve, but they're actually quite easy.
The following steps will teach you how to create a lightning effect:
Start with a light blue, gray, or yellow color as the foreground color. For this recipe, we have made the paper color black so that it is easier to see the light blue shapes.
Select a Pen(P) tool or a Brush(B) with a hard edge. Make the brush or pen tip large enough, and draw a rough shape of lightning on a blank raster layer.
Use the Hard Eraser(E) tool to refine the shape of the lightning. It should be angular and have areas of thick and thin lines. Here is a screenshot that shows an example of this refined shape:
Using a smaller brush or pen, add another jagged line along the first one. This should not follow the main line exactly, but should overlap. Refine the line as needed with the hard eraser. The following screenshot...