The answer is most likely by repetition.
But when you are learning from resources like 新完全マスター・語彙 which focuses on vocabs, of course we could understand and remember during the 1-2 hours of the study sessions, but I somehow doubt we would encounter 50% of the vocabs from there in other resources, or even daily conversations, due to the very specific/technical vocabs they are.
So rather than going back to the lesson book, I guess repetition might mean reading books (not lesson books)?
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The way most people do it is to use some form of SRS tool – e.g. [Anki](https://apps.ankiweb.net/).
Of course, reading is also a perfectly valid (and essential) way of reinforcing learned words – just harder to consistently get the same words repeated.
Anki or some similar software
I bought one of those 新完全マスター and then made Anki cards out of it and there ya go