The efficiency and comments part read like a tl;dr version of Kernighan & Pike The Practice of Programming[1], which, I might add, is an excellent read.
As for coding conventions, I quite like OpenBSD's (man style)[2], which are also present on FreeBSD. Though I rarely write C these days, I have to read some every now and then, and code from BSD projects following those conventions feels very readable.
[1] http://www.amazon.com/Practice-Programming-Addison-Wesley-Pr... [2] http://www.openbsd.org/cgi-bin/man.cgi?query=style&sekti...