I started off with a rough sketch like so - at this point I really only had a hazy idea of what I wanted going on in the background.
There were going to be some walls, and some potted plants, sure, but where would they be? What would they look like? WHO KNOWS. (I didn't!)
Using the sketch as a loose guide, I drew up some perspective guides in manga studio and started hashing out a clearer version of the image. The vague circle and square in the right wall became an alcove with some bottles and a vase, and the weird overhanging structure remained a weird overhanging structure.
I also started adding in some details to the areas of the background that were looking a bit bare - some paint chipped away to reveal bricks, a tattered rug...the extra potted plant was probably a bit unnecessary, in hindsight, but I like drawing plants so ultimately it stayed!
After hashing most of the background out, I did a color thumbnail. I tend to find that color is the most difficult aspect of these things to explain - I don't consider myself GREAT with color, and it takes me a lot of finessing and fussing to get a color palette I'm satisfied with. In this case, I knew I wanted the overhanging lights and floor tiling to be yellow/orange, and I felt the image would be best suited to a warm, inviting color scheme.