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What helped me was making a Google Sheets spreadsheet of all my letter pairs, and then making a Quizlet to study them. Memo went a lot faster when I knew the pairs off the top of my head, rather than having to pause and think about every one.
Hope this helps, good luck
The strategy that I used was to write down the letters on a whiteboard first, memorize them, and then execute blindfolded. After practicing doing this for a little while, I practiced doing it without writing the letters first, and eventually I could do full 3BLD.