In order to improve, you have to venture out of your comfort zone. For me is proper backgrounds, with perspective lines. Perspective lines are tedious, but fun as well.
For pixiv pocky theme contest -> [link]
I'm actually not eligible to enter but I was half way done when i read the contest rules OTL. Been entering quite a few contests for the sake of improvements and exposure.
my current room, but simplified, and added extras.
Poster in question