To draw backgrounds for comic books well, you need to have a good understanding of composition. Decide on the focus of the scene and arrange elements accordingly. Experiment with different textures and colors to make the background visually appealing. And don't forget to keep it consistent with the overall tone of the comic.
First, study the style of the comic you're working on. Then, look for inspiration in other comics or artworks. Sketch out rough ideas before finalizing the details. Use shading and highlights to give the background a three-dimensional look.