You can download it for FREE here https://blog.ahrefs.com/little-blue-book/
What make a link white hat? First, an important point... Google is not against all link building and not all link building is "bad". We can quote Matt Cutts directly on that from this 2013 interview with Eric Enge of Stone Temple Consulting. "No all link building is bad. The philosophy that we've always had is if you make something that's compelling then it would be much easier to get people to write about it and link to it. And so a lot of people approach it from a direction that's backwards." Indeed, Matt has pretty much defined for us the ethos of white hat link building - that links should be earned - not bought, or automatically created through manipulating loopholes. With every method included in this guide (save perhaps some social sharing) the editorial control remains with the linking website (either to approve the link, or to add it) and it is this editorial control that makes a link 'white hat'. But that's not to say we can't be clever too... OK, let's get started.