Especially if you need x64 assembly for performance optimization or during profiling a combination of godbolt (https://godbolt.org/) and Agner Fog's incredible PDFs at https://agner.org/optimize/ (especially parts 2, 3 and 4) are helpful.
The other useful step has been to write C functions and compile the code with a good compiler (good experiences with Intel, gcc and llvm) first at -O0 and later at -O2 or -O3 to understand how high level concepts can be translated to assembly.
This requires to have at least a basic understanding of registers and basic assembly concepts but at least has helped me apply the concepts to real code.
The other useful step has been to write C functions and compile the code with a good compiler (good experiences with Intel, gcc and llvm) first at -O0 and later at -O2 or -O3 to understand how high level concepts can be translated to assembly.
This requires to have at least a basic understanding of registers and basic assembly concepts but at least has helped me apply the concepts to real code.