Hello!
im not scene but i also make art so here something you can try
you seem to use a basic lineart brush and it's okay but trying a more textured/sketchy brush can help to get the messy scene look!
you can also try to use your normal lineart brush but set the opacity down a little and scratch your lines a bit more, the opacity will give the lines a layer effect idk how to explain
also if you want more scene elements maybe try some collage, go to pinterest or any other site where you can find images, choose the ones you vibe with the most and include them in your drawing as background or pop up elements !!
and as always follow your heart theses are just optional tips ahah
have a good day!