I purposely spend the most time and attention on the characters and backgrounds become secondary. Most of the time, I don't even have a background at all. To me, the characters in the drawing are the main part with scenery being extra. I see backgrounds as a bonus when I see one in arts. I think your backgrounds are really good. The only thing I can think of is, if you want them better than they already are, put more time in them if you want the backgrounds to be as good as the characters. That's all I can think of. It's how I would get better at doing my own backgrounds.