I struggle to remember precisely how we did .. I know we did.. I know it involved theater programs and phoning .. but the concrete memory is gone as if it was fantasy

There were these things called newspapers. They ran theater ads, at least a week in advance.

And/or, when you saw a movie, while you were at the theater, you'd just try to memorize the show times of any films you might be interested in seeing next weekend. Or you'd rely on what others told you about when/where they saw a movie.

And if all that failed (or you didn't even try), sometimes you'd just show up at the movie theater around 7pm without having done any research at all and see whatever looked good based on movie posters, titles, and actors you recognized.

Remember calling the theater's recorded schedule line? Then if someone bugged you at the wrong moment you'd miss the times for the one you needed and have to listen to the whole damn thing again?

Yes, I do indeed. That was an intermediate technology level. And in some ways, not so much worse than the Internet.

in my area we used to buy an aggregate journal of all theater programs, crazy to think how early on things were planned

There were these social networks called high school.