A quick way to make backgrounds more interesting, you can alter the strength of the final image by adjusting opacity and colours according to your needs.
Open up a new image and floofill it black using the paint bucket.
Next, go to Filter > Noise > Add Noise. Make the Amount 400, and make sure Uniform and Monochromatic are selected, then press Ok.
Now go to Filter > Texture > Patchwork, and change your settings to these:
Go to Filter > Stylize > Glowing Edges and use these settings:
Press D on your keyboard, then go to Filter > Render > Difference Clouds, and then press Ctrl on your keyboard and hold down whilst you press F to repeat. Do this as many times as you like until you get the effect you want.
Colourise and you’re done: