Productivity is a relative measure of output for a given amount of resource. If more output is produced without increasing input then productivity has improved. It's about being more effective and efficient, not just spending more time doing what you have always done.
In other words: Just do it.
 Systems and organizing frameworks for productivity, by career/role
It's been pointed out that the original GTD is chiefly for managers and administrators who do a lot of delegating, overseeing, bringing things up at meetings, and passing information back and forth between people. Other people in different lines of work have different workflows and different needs. It would be helpful to have a section which addresses these issues. (Feel free to move elsewhere... Also it would be handy to have a designated place for Proposals.)
Don't know where your time goes? Try time sampling.
Tailored for geeks and techies: