What I was working on yesterday. Room needs more furniture and clutter, and the lighting is really bad - I rotated the sun from east to west, north to south but the render result was always “boring”. So tips for better lighting are welcome. 
Nice work kratzdistel 
Not really an expert, but I think for the lighting you can add and play with more light sources (maybe put some indoor lamps), as for me depending on one lamp only and/or environment lighting seldom have a good effect on the scene. Also might want to play with light/shadow direction, as for now there are some windows on the scene but the light comes from different directions. Just some two cents from me, keep up the good work!
Thanks purbosky 
At the moment there’s only one environment hdri lighting and a sun light. Sun was originally for the shadows but that did not work as you can see in the render.
Maybe I really should add some indoor light sources and/or a tree outside for more interestig shadows. And an emission plane? Have to test it.
Nice Kratz! As for the lighting, definitely place around with the brightness and also you can try different color managements for it. Under render settings in properties –> color management and you can play with the view transform and look. Of course adjusting the lighting is probably first