Just one rule:
This is my first edited image. I tried to make the view of Io over Jupiter from an icy landscape on Europa (the FOV is tiny). Besides the color, contrast, glow and illumination anhancement of the edited version I've included redish aurora-like glows in the upper atmosphere of Jupiter, representing the Io-Jupiter electric current that indeed make strange plasma shows (but in the magnetic poles of Jupiter, not like in my picture).
Finally using these images I did the final edit.