I’m quite new to unity so I don’t know much about the software. I’ve created a room using free 3D models downloaded from the internet. Adding lighting in the room still doesn’t make the room look realistic enough.
I agree with Namey5 that the question is too subjective. However, I can advise something for you. The lighting is not only the thing that makes a scene realistic. Moreover, just adding it without the advanced setup will not make it either. You have to really get deeper into each single option of it.
Also, realistic scene has a lot of additional effect scripts and shaders. In my opinion, it is even more important than the professionally setup lighting. Usually, there is a standard list of effects that make your game look great (if you do not want any special visual effects).
The last moment that has to be considered is quality of models and textures. It is also very important. I have not seen your free models, but they must be made and textured with appropriate quality. Otherwise, it will look terrible regardless the previous points.
There is no tutorial that will teach you have to make a perfect scene from anything. You have to google and then learn different aspects of Unity’s visual effects.
For example,
Lightning setup (not tutor, but just to show you have much effort you have to make to setup lighting correctly)
Great Unity’s Adam (Scroll down. There is access to its assets. Unity provides you an opportunity to learn how you may create a high quality. Note that not everything might be used in real-time games due to limited performence).
P.S. Please, accept the answer if it helped you!