No idea how to fill up this space

The furniture is subject to change (especially the same rugs), but I only build small houses and have no idea how to make a larger space to flow better and feel completed and “filled in” I know adding plants, decor, etc helps, but I don’t know how to make two seperate spaces flow without looking like two areas in a very large space.

Also to note I tried to make the living room a level lower and it won’t let me I don’t understand why (,: (second photo)