Just look at your keyboard :-)

(https://en.m.wikipedia.org/wiki/ADM-3A#Legacy)

I always try to remember them by noting that the leftmost key moves left, the rightmost key moves right (not too hard), and that 'K climbs' (using alliteration to remember that). That leaves 'J' for cursor down.

In practice, though, I use the cursor keys. Luckily, they work on the editors/systems I work on nowadays. Side effect is that I am very bad at remembering those mnemonics.