I started with Anki(1), but had trouble sticking with it. I moved to a Leitner system with handwritten flash cards, and it’s much more comfortable to use — something about working with physical objects makes it much more effective. I’ve also played with the contents of the cards much more than I would have with Anki, because I don’t have to deal with the templates.

As it turns out, most of my cards are either Cloze deletions from known-good texts or reciting declension tables.

For the declension tables, I have one card for each row and column. That’s a lot of work, so I only have these for irregular words and a few representatives of each regular patterns.

For the Cloze deletions, I’ll read an article or a book chapter straight through without stopping to look anything up, and highlight 1 or 2 sentences on each page that seem interesting and come back to make flash cards out of them (and look up words I don’t know) after I’m done reading. Sometimes I’ll delete entire words, sometimes everything except the first letter, and sometimes drop the dictionary form in place of the declined one - The goal is to get my brain trained to choose the right word or word form without me having to think about it consciously.

For new words that aren’t obvious in context, I’ll look them up in a native-language dictionary. If I can understand the entry, I’ll make a Cloze card from that as well, usually just deleting any form of the word (especially the heading itself). In my dictionary, there’s generally an example sentence and I’ll transform key words there into dictionary form so that I have to remember which case, gender, etc I have to use.

(1) For learning Icelandic, not Korean or Japanese, but I suspect the concepts will transfer.