1. Be a genius. 2. All the other military theorists are wrong, wrong, wrong (and also, idiots). These two points quickly become tiresome as the main themes of this interminably long book. I have a pretty high tolerance for literature other people might consider boring, but this work really kicked my butt. Clausewitz makes some thought-provoking and tradition-challenging points, but for every useful bit of insight there are pages and pages about why no basic rules or principles can be applied to war, so the best idea is just to be a military genius who can magically measure all circumstances and eventualities and plan accordingly. Clausewitz draws from a very limited pool of military examples to illustrate his points and spends most of his time bashing the military theorists/strategists of the day (the book reads somewhat like a Facebook rant responding to the status “I <3 Jomini and Bulow”).
I have no doubt that, given time, Clausewitz would have polished this book into something more finished, consistent and useful, with less rambling, ranting and repetition. It is not his fault that he died too soon, leaving behind only a rough draft, but as it stands, I think he would be embarrassed to see his work published in this condition. While the work does have a lot of historical value, this is a rare case where I would advise would-be readers to save themselves a lot of pain by skipping the book and instead reading a good commentary and some thoughtfully-chosen excerpts.