What was it like? I'm planning one for here in my small town.
I've been to quite a few. This is all IMO.
They've ranged from "cheap wine, bad cheese" in a basement (under a lovely bookstore) to televised gala things. Some of the best ones I've been to have played with the format a bit - like one for a book involving social media that had a chat about social media with some local experts as well as a reading. It's nice if there's a connection to the book somehow.
It's a fine balance for timing - most people are there for the author and want to hear a short reading or interview or even a little bit of both, but if it's long, it gets boring and awkward. I'd aim for 15 minutes. A lot will depend on whether the writer's witty or whatever. But a good celebratory mood is best.
Venue: It should be public (not a private home) and it's nice if it's a nice space, and double good if it promotes a local business. Consider seeing if other local businesses want to be on board to promote themselves, especially if they fit in with the book itself. (They might give you a discount on catering or something.) I'm sort of ehn on door prizes, but they can be nice.
Leave time for signing, and make sure there's good space for signing and lineups. Have copies of the book to buy (order forms encourage procrastination); it's nice if there's a discount at the event. Make sure there are nice pens available. It helps sometimes to have people write names on stickies if they're asking for dedications to speed up the process and not have the author have to ask how to spell Aidan/Aden/Aeden/Aydyan a zillion times.