When I first started out with C (and back at that time it was the first programmimg language I started learning) I read a majority of the "standard" books and felt rather confident in my understanding of the basics, but when it came to actually writing C, I never felt like I was writing good, pragmatic code. So I started combing through the sources of popular FOSS software like gtk, musl libc, Linux, OpenRC, gcc, etc, submitting bugfixes for a few of them, and asking for code reviews on mailing lists until I finally thought that I was doing okay. I still felt like my knowledge was lacking though, so I decided to learn the internals of the modern x86 machine by writing a hobby OS resembling MINIX (I think I even got X working at one point). Despite still not being the best programmer, it really helped with my understanding of why things are done in C like they are.