When I first started down the path towards my writing career, my mentor Gary Brent told me about his strategy for being productive: He would reward himself for completing some milestone---a project for a class he was teaching, perhaps, or a chapter or section of a book---by playing videogames. It was a simple system: Get some writing done, play videogames for a little while.
This first came up while we were working on an update to a Microsoft Excel book that he had written for the education market. Strictly speaking, the first book we worked on together was about Visual Basic 3, and that was my entry into writing as a potential career. But he had previously written the Excel book alone and the publisher needed an update for whatever the then-most-recent version was. And so we worked on that together as well, with me in a decidedly minor role.