1. Room Lighting
2. Object Emission
3. Background
1. I used MagicaVoxel for this piece (sometimes I export to Blender). During rendering, I like to add light using "emit". You can play around with the angle. I used 60 degrees by 30 degrees for indoor spaces (because I like diagonal shadows), but it will depend on your piece. Cast the Area to 0 if you are looking for dark-casted shadows, and adjust to windows and objects. Set the Intensity to 100 if looking for high contrast.
2. In dim rooms, I use brightly lit points. Material Emission can be set to 100, and the power set to 2. If you are wanting an incredibly bright light, set the power higher. I usually use 2-3 in order to keep the color. Explore different color variations and contrast.
Change camera views to find interesting angles.
3. For the background, I usually have two colors for sky and ground, with a blended horizon. Sometimes I choose different shades of one color and fade them for a dark and "enclosed" atmosphere. You can choose anything you want - have fun. Lol. For dim rooms, increase vignette.