Tackling the background
Just as I did for correcting things before, here I put a layer above my canvas, which I fill up with some lighter colour and then lower the Opacity. Now on another layer above again, I use a hard-edged Round brush that’s set to 80 per cent Opacity to roughly sketch in some characters and the ongoing battle in the background. I then delete the layer in between, so I only keep my lines, which I also lower the Opacity on, and quickly block in some values. This will all stay pretty rough and blurry because the background doesn’t play a big role in the picture: it’s just there to add some storytelling and enhance the overall mood.