They wanted you to have a plausible manner, an appetite for long hours and, ideally, to have watched a few ads. The entry system was largely interview-based; this enabled employers to check out point one pretty directly, ask questions about point three and have some good guesses about point two. (On the basis that if you were lying, but convincing, about point two, then you'd gain extra marks on point one.)
This didn't apply to creatives, of course. They had to spend six months at Watford or be related to someone famous. And the people who did the actual work - production, finance etc - had learned their trades at proper colleges.
But then, and for a long time since, advertising was broadly a business of watchers and talkers, with a light sprinkling of thinkers. We would observe things and talk about them. Ads, businesses, consumers, director's reels, trends. Most of our everyday activity was noticing things and discussing them.
Our unit of useful production was the meeting: meetings with clients, meetings with production companies, meetings with each other. It's significant that planning couldn't really get going as a trade until it invented the focus group - a way of having meetings with consumers.
Our expertise was largely abstract: we saw things and we talked about them. Production companies did the practical stuff, or printers did, or exhibition companies or DM houses.
We rather looked down on them; we'd managed to make abstraction seem like the highest form of activity. Perhaps that's why we envied management consultants so much; they were even more abstract than we were. And perhaps that's why we missed the internet so badly. We were good at looking at it and talking about it, but we never understood it properly because we rarely did anything with it; we never tried to make stuff.
Nowadays, though, that won't do. My nephew's going to graduate next year, and I suspect he's interested in the marketing/media/whatever world, so I've been encouraging him to learn as many doing skills as he can.
Yes, he needs to be able to present and talk well, but he also needs to understand modern media as a maker, not just a watcher. So he's making videos and learning some CSS and experimenting with materials, and I'm nudging him to try some Processing and Arduino coding and to experiment with 3D printing and some robotics. Not so he's an expert in all those things, but so he understands them from trying rather than watching.
That's what I'd encourage today's graduates to do - to be able to say, when asked about some new technology: "Yes. I've done that" rather than "Yes, I've seen that."