Programming style

A classic, but nowadays little known, book that teaches how to program more effectively is The Elements of Programming Style by Brian W. Kernighan and P. J. Plauger. Although the book was written before the development of many new-fangled programming concepts such as object orientation, its precepts are universal and still well worth consideration. It's also gratifyingly short, so it's a quick read.

The book itself is likely out of print and may be hard to get hold of. However a web search will probably turn up a link to a PDF. The Wikipedia page also has a succinct list of the most important ideas.