Well, as I study yet another tech book, this one on AMP Web Development I find that pre-view, PhotoRead, gestate a trifle and then slowly digest important 'first ideas' that I think may the lay the foundation of use and understanding to be my preferred methodology.
Generally, this salient info is mostly to be found in first chapter or two, summaries and any glossary or legend key where terms are listed.
Next is use, I just do not see mastering information unless that definition of mastery includes adroit use.
Why else know it? Technical data begs for a application of its detail and it is that very detail that makes it seem so cumbersome.
I like dipping, but I where I find a key point I slow to a crawl for a few minutes and meditate on the significance of the idea involved, shut the book for a bit and go do another task on other subjects before picking the book up again and repeating.
This goes on for a few days until I get the feeling I know it and I leave it be until I have direct use for it. And I do not think it matters at all, how much time goes by, you could pick something back up years down road I reckon.