I feel K&R is an important classic from which one can still take a lot of valuable jewels in a pretty concise way. If possible, complement it with other books like Peter van der Linden's Expert C programming (although I don't like his opposition to static linking).
If possible, check the suckless.org projects, they tend to have pretty idiomatic and clean source codes.
If possible, check the suckless.org projects, they tend to have pretty idiomatic and clean source codes.