You need to have a clear understanding of the overall style and theme of the comic. Then, practice observing real-world environments for reference.
First, decide on a consistent art style for the backgrounds. It could be realistic, cartoonish, or something in between. Then, pay attention to details like light and shadow to maintain consistency throughout the comic.
To draw consistent backgrounds, start by establishing a set of rules for perspective, color palette, and level of detail. Also, keep studying different comic styles for inspiration.