We recommend reading everything about software testing by the following authors and anyone they recommend:
Four Schools of Software Testing
Bret Pettichord’s Four Schools of Software Testing describes five distinct approaches to software testing and helps us understand why some testers fundamentally disagree on so many topics. For example ISEB / ISTQB promotes the Standard School approach, whereas Test Partners is in the Context-Driven School.
There are five schools but the document title refers to four because the Agile School did not exist when it was originally written.
Context-Driven Testing is a one-page website that includes the Seven Basic Principles of the Context-Driven School, some examples and comparisons with other approaches to testing.