Anki deck philosophy
I have developed my own philosophy regarding Anki decks, which I think is pretty different from the typical ways in which Anki decks are organized.
how to split anki decks: the intuitive thing most people do is to try to split decks by the subject matter. so you have one deck for math, one for history, one for random facts, etc. but i think this is a mistake! you should split decks by the following two rules: (1) each set of cards that requires a different review schedule should get a separate deck (e.g. you want some cards to be spaced much more aggressively, or you don't want to re-see a card after you make a mistake, which is the case for me with proof cards); (2) if you want to prioritize some cards over another, you can set up separate decks so that you only get e.g. 2 new cards from a low-priority deck but 10 new cards from a high-priority one.
these rules lead me to have separate decks for math problems (want to space longer, and don't want to see mistakes), incremental reading (ditto, but with slightly different mechanics), and then two-tiers of regular cards ("everything", which is for low-priority stuff like kanji, and "high priority" for technical subjects mostly).
in other words (simplifying this to a single rule now), you should split decks by the things that you change in the "options" menu. the card type can vary within a deck, but the card review mechanics cannot change within a deck, so cards that should have different review mechanics should be placed in separate decks. Importantly, if two cards are about different subjects but can have the same review mechanics, you can place them in the same deck. And if two cards are about the same subject but have different review mechanics, you should put them in different decks.
I now have four "math problems" decks (for doing spaced proof review). the first is the original one, which i stopped using because of the stupid 160% default easy factor, and which now has 75 due cards. the second deck is the place where i moved all the new cards to, so that i could start going through the backlog of new cards i made. this one is working fine i guess — no big problems so far. the third deck is to address the fact that i want to add new cards even now, but if i add them in deck 2, then i'll be reviewing them in like five months or whatever, which seems a little too far off. so i'd like to add new problem cards, do a "fake review" or something (since they are so fresh in my mind, i don't really need to re-solve the problem), and then have them come back in one month or so. And now that the third deck started having due cards, I decided I wanted a fourth deck where I add new cards and move them back once I do the fake/empty review.