*sorry for my bad english 
The simplest way - use some ready (you can download free textures (choose all maps) from here: https://texturehaven.com/ PBR textures on the walls:
step by step - UV unwrap the walls, give them new material - if you use Cycles - then open Nodes editor and add textures (like diffuse, Normal Map) to proper slots. Also, see this tutorial: Blender Guru PBR tutorial
If the walls are supposed to look painted, then you could add a very small noise bump to them (to simulate the slight stippling effect you get from a paint roller).
You could also try using the microroughness node group, to add some slight reflection variance to the wall.
I used this effect on a scene I downloaded from blendswap in the link below. The effect is subtle on the walls, but IMO definitely adds some realism.
Walls are not a flat painted surface, they have imperfections, and as noted, a very slight bump.
It may not sound like much, but it makes a world of difference.
For flat walls like these, unwrap might not be required; box mapped might suffice. Unwrap will be required if you plan to bake stuff though.
But yeah, microbump and to some extent roughness maps will help. Maybe even a tiny bit of huge bumps to make it less complete flat.
“PBR” textures does not always confirm to PBR cheatsheets. For best results, match the albedo of the texture (or color) to that in the PBR cheatsheet.
You may have to work on the other materials as well if they end up looking too bright. Lamp should be set to ~real values, and then the exposure under the scene tab should be adjusted to suit - set filmic as well if you haven’t already.
In addition to the other suggestions, your corners (e.g. the edges of the table) are completely sharp. In reality, nothing is that sharp - you want to add a slight bevel even to sharp corners. This will catch the light, and look more realistic.
