What you should focus on: think through what of your work might be of broader interest to the public. Is your research interesting and on timely topics that the public cares about? If so, be ready talk about that. Are you innovating in teaching in a way that might be of interest to the public (maybe, teaching an unusually large class; teaching a MOOC; teaching a topic of broad interest; trying some innovative new experiment)? If so, be ready to talk about that.
Do not plan on giving a talk. Don't rattle on. The PR rep will ask questions and ask for more details. But be prepared to give a few highlights (a few sentences) on one or more areas like this, if they might be of broader interest.
If you don't have anything that might be of broad public interest, that's fine, too. Go in to the meeting preparing to learn something from the PR rep, rather than the other way around. Ask them to give you a brief tutorial on how to interact with the press. If you're interested in it, ask whether they have a media relations training program. Meet the person, and treat it as a networking opportunity to build a relationship you might use someday.
But overall: Don't overprepare. It's not worth spending a lot of time preparing in advance for this one. Go into the meeting, see how the PR rep can help you and how you can help your university, and move on to something else in your busy life as a professor.