Tangentially related: I have found the ease of creating cards one of the most important factors determining the speed at which I learn. For example in anatomy, I started with making cards from a photographic atlas, but this took way too long. (I still desire to make cards from them, since they use actual photos, not simple schematics). For the later, I had to manually cut out the images, and extract the labeling. In contrast, what I ended up using was Gray's Anatomy for Students Flash Cards. It's a 817 page book, with most of it in being alternating pages of images and corresponding names.

This was much easier to make (digital) flash cards from. With pdftk, I could separate the pages into a file of all images and a file of all assorted labels. With pdftotext I could easiliy convert the pdf of labels into text (which I could simply, ~automatically form into flash cards) while I used imagemagick to extract the images themselves. (with all the borders, etc, cut off.) (while I have done a part of the conversion process manually (some names were split into multiple lines, and there were minor irregularities in the text format of the file, so I manually made each section into a separate flashcard (Inserting headers of a card, deleting newline characters if splitting an item into two, and marking the beginnings and endings of clozes), but I am certain that that could've been easily automated, with a proper understanding of regexps. (learning which would've been more economical on my time)). With all this, it took me 13 days until I had first exposure to all 3630 cards, probably significantly less, than if I had to do everything manually.

So, whenever you can, automatize.

(Before this, I used to extract glossaries of books manually. Obviously, I use the same tools for that too, now.)

I learned to love books which had great glossaries, and great summaries. Some are so great, that by reading the summaries, you don't even have to read the actual chapters. (Which may be artificially inflated in length because of a length goal the publishers set, or because it is more targeted towards entertainment value, than for quick conveying of the ideas behind them. A quick skimming may still be worth it, though, even if in preceding chapters you established that their compression is pretty lossless.) Only tables are better.

One thing I want to add to my current toolset is a way to automatically extract wiktionary definitions: sometimes the whole idea is in there, but either way, speaking the language of your desired subject by the time you encounter the more in depth books is handy. (this, coupled with a trickle system, AKA (~20) word(s) of the day)

I used to try to avoid duplicate cards, but I learned to love redundancy.

Also, mind sharing your cards for the holonyms?