Before goodbye, name one specific thing in their life with a rough timeline that you'll check back on, write it down, and follow through.
The idea
I've watched a couple of people do something clever at the end of a conversation: they close with something specific to check back on. That's an open loop. It gives you a built-in reason to follow up, proves you were listening, and tells the other person you expect the relationship to continue. "We should stay in touch" has killed more relationships than distance ever has.
How to do it
While you talk, listen for something coming up for them: an event, a decision, a trip.
As you wrap up, say you'll check back on it, and roughly when.
Note it somewhere you'll see it again.
Check back. The loop only works once you close it.
Example
Say someone mentions they're heading to Portugal. You ask for a full restaurant report and jot "Portugal, restaurant report" in your notes. When you reach out later, you have an actual topic: the trip.
Script
"You mentioned your daughter's soccer tournament is next weekend. I'll check back in to hear how it went."
"Good luck with the board meeting Thursday. I'll check in Friday."
"Let me know how Portugal goes. I want a full restaurant report."
Watch out for
Each loop should be specific, have a rough timeline, and be about them.
Listen for Their Ask: People hint at what they need in passing. Capture their "ask" after every conversation and offer help before they think to request it.
The Follow-Up Question: Find the most interesting thing about someone that they don't lead with, ask about it, then ask a follow-up. Don't pivot to yourself.