The specific shared fact
Remember: my [SPECIFIC THING: dog's name, job, hometown, a tattoo, a song we both like]. Reference it unprompted in the next three conversations where it's relevant.
Why this works
Persistent-memory engines need specific anchors to latch onto. Generic facts ('I like music') don't stick. Highly specific facts ('my dog's name is Muffin and she has three legs') do.