Well for me a couple of things either reinforced or added to what I had already knew/learned
I wont say to much as I think i wont be able to do the book and the people who produced it justice, and it would be nice for us to support the people who put out good material like this website.
1)breathing - slow deep breathing is important as it helps slow and relax the nervous system
2)intensity - dont stretch to hard or feel sharp pain when stretching it should be easy and relaxing
3)assessment - they go over how to assess ones own or another flexibility. When you know what is tight, and most are suprised where they think they are flexible they are not
4)sling - it talks about the fascial sling and a brief overview of anatomy trains (another good book)
5)sport specific stretches - the book has sections for different sports and has a map showing which sports require which areas of flexibility.
The best concept out of the book that I could say is that and this relates to the beginning of this thread. Is that the body is connected and if your hips are tight it might not be due to having tight hips, it may be due to postural alignment or other surrounding and connecting muscle that are tight. And when those are corrected youll find youre hips to release.