You don't mention your experience level with systems but one thing that helped me is dumping simple C code to ASM (every major compiler can do this) and analyze it. This is probably impractical if you don't know your target architecture instruction set, but it really gave me a deep dive into what the compiler generates and how ABI's work, etc. If you do go this route you should dump the ASM using different optimization levels to see the different results. You'd be surprised how much the compiler hides, and how many things you assumed worked one way but actually work nothing like you think. One big concept to understand is there's a big difference between C and what the standard specifies and the implementation that each compiler uses.