to make my work more fast i reuse same background this many times as I can. At first I draw full background and put it wherever it fits to that localisation or I blur it a little bit.
Sometimes I also reuse same lineart from previous chapters but I give a different shading and composition of scene, or different face expression and it looks like it's freshly drew
I make my own brushesh for exaple some flowers, patterns or I use those from clip studio assets it's really makes your work faster
I also use 3D models for interiors or buildings, I paint on them either way, to make them look, I did it all by myself, but it's way easier than do it from the sketch