In my experience, even if it's a full week-long jam. It is preferable to do a simple concept with highly restricted audiovisual content.
I have a base template I made for my pixel art games, of 512x288 pixels (16:9 ratio, from 32x32 px. squares).
Besides that, I start by selecting a color palette that relates to the emotion I wanted to convey. Usually I use one with between 8 to 24 colors, choosing it from Lospec.
Since you already work with chiptune, it should ensure that the music has the right fit.
What other kind of thing do you want to work on during the jam?