First start with this article:

And then read this one:

The short answer is that there are some rough patterns that you can learn from that Tofugu article that may be helpful, but that you do need to look it up basically all of the time (you can have Anki do it automatically if you tinker with it a bit - ).

To better memorize which one goes first, I like doing the Kanji Signature thing, or honestly even better, I like creating NEW radicals for every combination of *two* radicals I see. That's been what I gravitated towards in my last couple of months with Japanese and it's what I'll continue to do once I get back to Japanese at the end of this year.

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