I am not really an archviz expert, but based on seeing huge numbers of images, I would start with the basics - an image won't look good as a whole if materials, models, and lighting do not look good and realistic. If we take any of the items in your images, for example: the tree, the water, the background image - it is obvious that it's CG. I would also try with a few different HDRIs for lighting, and different post-processing options (especially LUTs) to get more interesting and less generic atmosphere in the scene.