Playing to Win: Becoming the Champion is a book written by David Sirlin with the purpose of "teach[ing] you to win." The article was linked by CronoDAS's LessWrong article "Playing to Win". The term "playing to win" comes from Sirlin's book and can be described as using every means necessary to win as long as those means are legal within the structure of the game being played.
The first step in becoming a top player is the realization that playing to win means doing whatever most increases your chances of winning. That is true by definition of playing to win. The game knows no rules of “honor” or of “cheapness.” The game only knows winning and losing. (Emphasis original.)
Sirlin also shows a contrast between people who play to win and scrubs who do not.
The scrub [...] is bound up by an intricate construct of fictitious rules that prevents him from ever truly competing.
An example of these fictitious rules can be found in the video game Street Fighter. Scrubs often consider repeating the same moves over and over as a "cheap" or unworthy tactic and will refuse to use them even though they are legitimate strategies.