I organized it in a third place (not sure about how it's called in English, "tiers-lieu" in french), they did most of the communication. I also gathered e-mails of people interested on foss and related subjects during other events and I send them e-mails everytime I throw an event.

There are some initiatives like End of 10 which gather local organizations that might throw install parties, that can help being visible. There are probably others but it depends on where you are.

On the practical level, we prepared a quick slideshow that we run in the beginning to show people why they'll love linux (talking about free software philosophy, and why proprietary is not a good idea) and then we have half a dozen Linux mint keys that we share with everybody and we all run the install at the same time.

We also bring a couple more keys, like a gparted and/or debian live just in case we need to do some recovery.

Most of the people completely switch from windows to Linux but we had a couple of dual boot. We also had one impossibility due to the person wanting a dual boot and their PC using a weird RAID controller preventing us to repartition the disks, or install grub, I don't remember.

Anyways, it has been a lot of fun and I recommend anyone competent to try, it's really nice to bring linux to more people!