I believe that @ftornay’s advice is good. I might suggest that you focus on one case at a time. During your “genitive week”, e.g., read about that case, its uses, and the prepositions that require it. Continue your reading, but paying especial attention to uses of the genitive. Likewise with the other cases, but each in turn. It’s hard to concentrate on six things at once.
@Ericb100’s advice to write is sound. When speaking with people you cannot pause and think and perhaps consult a reference, but you certainly can when writing. Eventually that work with writing correctly should be reflected in your speaking. If you want you can even submit your writing to a tutor for correction.
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