As an American teacher of high school English, with a passion for spaced repetition software, I feel like it is my duty to respond to this post. My answer may surprise you.
If your goals are simply to understand more of what you read and to write more effectively, trying to skill up your general English skills strikes me as rather suboptimal.
Sure, a mastery of common word fragments will improve your ability to make at least some sense of unfamiliar words that use them -- I certainly teach these -- but you probably already know the most useful ones. I’m also unconvinced that etymology deepens comprehension much; usually, we want to understand someone, not somewords; this comes from understanding what that person intended to communicate, not from unlocking obscure arcana behind the words they happened to use.
Most of what is known to help reading comprehension is language independent, as is most of what is known to help you write better. I certainly don’t think Paul Graham’s skill as an essayist has much to do with his English; if he knows a second language even marginally well, I’m sure he would write in it nearly as effectively. To wit, he eschews esoteric explication. Writing is a craft, not a lookup table.
The strongest predictor of how well someone will do on a comprehension test of a given passage is how much they already know about the topic of that passage. A knowledge of the domain-specific vocabulary for that topic is either the second strongest predictor, or the same thing, depending on who you ask. General purpose vocabulary is farther down the list, and as an educated native speaker, you, again, are unlikely to find much low-hanging fruit in that area. So rather than take another level in English, I would suggest you consider which domains you want to be able to understand more of, and just start reading more in those domains, looking up words as needed. The language you do it in is almost irrelevant.
Consider: in the 6 credit hours of theory and practice for teachers of English Language Learners my state requires all teachers to take, I was taught that teenagers acquiring English as their second language are best off when they can continue learning domain specific concepts in their native language while waiting for their English to mature enough to transfer this knowledge over. Otherwise, they gain conversational English fluency but miss out on their first, best chance to learn foundational abstract concepts in, say, Science, Math, or Social Studies, leaving them without the ability to talk or even think about these subjects in any language.
With all the above in mind, when it comes to Anki cards and vocabulary, I am convinced that a great example sentence is much more useful than a great denotative definition. Connotations matter, and a visualizable, narratable context goes far both in conveying the extra implications of a word and in providing hooks for one’s memory. Still, you’re unlikely to absorb the deep flavor of the word -- the full intent of one who wields it fluently -- without encountering the word many times in varied contexts.
I say this in part because I acquired a sizable Spanish vocabulary from a time living in Spain decades ago, and there are to this day a number of words common to my internal monologue that are Spanish simply because they capture the flavor of the concept more perfectly than my closest English equivalents. But this is only the case for words that I encountered on enough authentic occasions to build that full connotative sense. Ones I merely studied out of the dictionary never reached that level, no matter how well I mastered them from a recognition and recall standpoint.
As any programmer will tell you, leveling skills in one language will have knock-on effects on your abilities in other languages, whether they are similar or not; the similar ones give you skills that transfer very directly, while the dissimilar ones broaden your conceptual toolset for approaching programs in general. If a problem might be more tractable within the intricacies of language suited to it, by all means, go deep into that language. But if you’re trying to understand say, an algorithm or a data structure, study that.
I’m also unconvinced that etymology deepens comprehension much; usually, we want to understand someone, not somewords; this comes from understanding what that person intended to communicate, not from unlocking obscure arcana behind the words they happened to use.
Perhaps "etymology" was a misleading word choice. I didn't mean to suggest that it would be useful for me to develop a deep historical understanding of how English words evolved. Instead, I was referring to the simpler task of learning to reliably see the parts making up English words....
I've spent many thousands of hours over the past several years studying foreign languages and developing a general method for foreign-language acquisition. But now I believe it's time to turn this technique in the direction of my native language: English.
Most people make a distinction between one's native language and one's second language(s). But anyone who has learned how to speak with a proper accent in a second language and spent a long enough stretch of time neglecting their native language to let it begin rusting and deteriorating will know that there's no essential difference.
When the average person learns new words in their native language, they imagine that they're learning new concepts. When they study new vocabulary in a foreign language, however, they recognize that they're merely acquiring hitherto-unknown words. They've never taken a step outside the personality their childhood environment conditioned into them. When the only demarcation of thingspace that you know is the semantic structure of your native language, you're bound to believe, for example, that the World is Made of English.
Why study English? I'm already fluent, as you can tell. I have the Magic of a Native Speaker.
Let's put this nonsense behind us and recognize that the map is not the territory, that English is just another map.
My first idea is that it may be useful to develop a working knowledge of the fundamentals of English etymology. A quick search suggests that the majority of words in English have a French or Latin origin. Would it be useful to make an Anki deck with the goal of learning how to readily recognize the building blocks of the English language, such as seeing that the "cardi" in "cardiology", "cardiograph", and "cardiograph" comes from an Ancient Greek word meaning "heart" (καρδιά)?
Besides that, I plan to make a habit of adding any new words I encounter into Anki with their context. For example, let's say I'm reading the introduction to A Treatise of Human Nature by David Hume. I encounter the term "proselytes", and upon looking it up in a dictionary I understand the meaning of the passage. I include the spelling of the simplest version of the word ("proselyte"), along with an audio recording of the pronunciation. I'll also toy with adding various other information such as a definition I wrote myself, synonyms or antonyms, and so forth, not knowing how I'll use the information but by virtue of the efficient design of Anki providing myself a plethora of options for innovative card design in the future.
Here's the context in this case:
With the word on the front of the card and this passage on the back of the card, I give my brain an opportunity to tie words to context rather than lifeless dictionary definitions. I don't know how much colorful meaning this passage may have in isolation, but for me I've read enough of the book to have a feel for his style and what he's talking about here. This highlights the personal nature of Anki decks. Few passages would be better for me when it comes to learning this word, but for you the considerations may be quite different. Far from different people simply having different subsets of the language that they're most concerned about, different people require different contextual definitions based on their own interests and knowledge.
But what about linguistic components that are more complex than a standalone word?
Let's say you run into the sentence, "And as the science of man is the only solid foundation for the other sciences, so the only solid foundation we can give to this science itself must be laid on experience and observation."
Using Anki, I could perhaps put "And as [reason], so [consequence]" on the front of the card, and the full sentence on the back.
What I'm most concerned with, however, is how to translate such study to an actual improvement in writing ability. Using Anki to play the recognition game, where you see a vocabulary word or grammatical form on the front and have a contextual definition on the back, would certainly improvement quickness of reading comprehension in many cases. But would it make the right connections in the brain so I'm likely to think of the right word or grammatical structure at the right time for writing purposes?
Anyway, any considerations or suggestions concerning how to optimize reading comprehension or especially writing ability in a language one is already quite proficient with would be appreciated.