So you can have gradients, solid colors, or patterns/textures (you can find tons of freebies on the internets) to establish the mood of the characters or the environment. But as was said, you will want some establishing shots of the environment. A good thing to keep in mind always is the positions of your characters relative to each other, even if they move. EDIT: this is important even if you minimalize your backgrounds in later panels.
As for backgrounds, if your art style has more realistic proportions, you may want to consider using free 3d stuff like sketchup. I've used it myself a bit in my comic but I think I'm going to make my backgrounds more painterly and by myself moving forward. I might still use it to make my own buildings that I will use very often and want to be able to get different angles of quickly and easily.
Unfortunately even with easy cheats like that, there is no one-size fits all situation and there will come many points where I'll have to draw everything myself the old fashioned way. Like @AnnaLandin said, there's no getting around the need to improve your skills to draw what you have in mind.