When I am wearing my academic hat, my technique is to first gather an enormous, excessive amount of material, including every book, paper, file and website I can download or haul from a library and skim abstracts, tables of contents, and titles to get a map of the topic in my head. I may only really read one or two of these references in detail. I sometimes put high-value nuggets of information in Anki. One critical thing for me is that this process is highly active and I must be feeling energetic. Reading technical material is not a sedate, passive experience for me, and if I am bored, my interest and thus my retention drop to zero. Thus, it is essential that I be sufficiently curious about the topic at hand that my curiosity powers me through the process. For me this is a critical part of my process.