Read the C Programming Language (C Bible) Kernighan and Ritchie for OO and Procedural programming (K&R Style is about 50-50 in that area, ANSI C is more OO). Another is SICP (and the Lisp videos on said site) and/or The little schemer for functional programming. Donald Knuth's The Art of Computer Programming series as well as Design Patters by the gang of four (Gamma, Helm, Johnson and Vlissides) are also must reads for general algorithm and structure.
Other than that, doing a program or two on http://www.spoj.pl/ every few days will help, since that is a "competition" site and gives good feedback on your program results.
Practice doesn't make perfect - Perfect practice makes perfect.