This is the first time we are running this sort of event, so the procedure might need some debugging, even on the fly, but this is how the evening will proceed: each person will write what they want to work on down and next to it their name. If you see something you'd like to work on the list, just add your name to it or go and introduce yourself to the other person. If you are both happy to work together, find a space, sit down, and code away.
If you are new to pair programming, there's some blog posts you may find useful:
If you are new to Clojure, no problem! You can team up with other new clojurians to learn together or have a more experienced one help you. I'd advise against jumping into projects that are too complex as it can prove frustrating for you or your pair programmer or both.
The projects can be anything, such as: building a library, building a pet project, work, figuring out something new. If you don't have a project, that's not a problem as you can just join someone else that has one. Even if you don't have a project or a laptop set up, do bring a laptop computer as it can be useful to check documentation.