[jmercan]

I would say "Effective C" is a good book (and Robert is awesome) but personally I feel like I learned the most by writing and disassembling small quines under different compilers and flags more than anything else.

Also, reading through some codebases gave me good (and horrible) ideas and habits. However, C projects are usually messy and I am not sure whether recommending it would be helpful or just confusing. But I would say TenDRA, BearSSL, pkgconf, s6, kivaloo, apk-tools, libsodium, musl, OpenSSH and cosmopolitan libc are worth checking out.

Finally increasing my tiny understanding of architectures, memory models and decades of safety issues was significantly helpful as well.