It's hard to beat this list of quality books:

http://iso-9899.info/wiki/Books#Learning_C

Read some and do the exercises. You'll learn to write portable code to a standard rather than stuff that "accidentally works." There's a lot of crap C code in the world, full of GNUisms, overzealous macros, header-only nonsense abusing translation units, and copypasta. Don't pick up bad habits from that stuff.