Well this is a question with no real answer. I’ve used UE4 for a few years and I still haven’t achieved photo realism albeit, I’ve gotten close. Its really a fact on
Practice,
The Artistic eye
and knowledge of advanced material functions.
If you browse the UE Forums, there are free examples in the community content section. Some of those are great teachings on how to create good materials.
The artistic eye is something that you slowly learn and use. Its mainly learning what to “see” in the real world and then learning to “apply” in your fake ones.
(i:e seeing just how metal looks when its scratched and then learning how to do scratches properly inside the material editor)
Using advanced material functions is a pain in the a** the tutorials on these are not great, and the documentation is equally frustrating. It’s just a matter of reading, seeing, doing, and redoing. Trial and error. And eventually it will come to you.