I remember you saying that you were working on a book project! After starting (and pausing) a couple of times in the past, correct?

Actually, I'm currently working on two books - but this one is more important right now, since the amount of work I already put into it is quite big. And I really want to finish this book, because it covers a lot of topics which are important for me as well.
Besides that: I would like to put into my CV one day the phrase "I wrote book XY" :)

"How do you go about writing a book?" This is, without a doubt, one of the ambitions I have in life. Still, I have no idea of how to start. I feel I have so much to say, but don't know how to go about structuring and selecting what I wish to address.

I think, this might be different for each author, but for me it was really helpful to start with simple notes about different topics I want to cover. Then you can start to build a basic structure around these and think about how to present the content. If you know you want to start with X and finish with Z, then it's easier to build around that basic idea.
During the writing much will change regarding the details, but the big picture often remains unchanged.
Then "just" start. Tell yourself to write at least one paragraph each day (currently, I've set my personal limit with at least 1000 words/day) and before you know it, you might have written three. The important step is always to actually start. Each day. Even if you don't feel like it. You can edit afterwards anyway, but it's a good idea to make a habit out of it.

Thank you for this post Ego. I will be eagerly following the toolkit series :)

I probably have to disappoint you here - I will not write about the tools extensively. At least not until the release of the book and even afterwards probably only in form of smaller parts. Never give your USP away for free - economics 101 :P