Before we really dig into exactly how to skin this cat, we have to talk about what can be the hardest part - getting people to show up.
If you don't have an identifiable community in your area, don't go in expecting that hosting narrative events will build one out of nothing.
I could, and may, write a whole article about building a local community. This is not that. If you want a community, build that first, and don't expect running a narrative event to be the solution.
If you have no reason to believe a given game has any pull with the folks near-at-hand, I'd recommend starting with just playing what's out there and forming an organic network before you dive in and start hosting.
You can still try. I'd love to be wrong.
If what you have is wargamers, especially those who sit around and openly bemoan the lack of weird shit in the area, your work is half-done, sitting au naturale in the local ecosystem - you probably know what you need to do, but like staring at your own personal Green Goblin mask, you may be afraid to do it.
There's basically no way to sell something free without seeming a little unhinged. Just posting flyers and leaving cool, detached discord messages will only get you so far.
The instant what you're doing starts to feel like spamming, that's when you know you've hit a sweet spot.
Once you become convinced any number of people have seen your advertisement enough times for it to be annoying, that's a good sign that it's getting in front of eyeballs, which is really all you can do.
As far as specific tactics go, hobby discords and bulletin boards are the bare minimum.
Free stickers and cool flyers or zines are the next step from there.
If you already have a local group of dedicated weirdos, then this section is mostly just filling for a bird cage. As the saying goes, "ask a punk", and the rest will follow.
With that out of the way, lets dig into some gory details.