Since I once said that you should write an article if you're doing something like this, here is one:
We're doing another one of "these things" (terminology pending). It's called #dance-macabre, you're free to post your own images to it, and this time we're not even pretending it has anything to do with a day. If you've taken part in something like this before (i.e. #foxyfriday, #nunday, etc), that is all you need to know, otherwise read on.
So what is this
It's sort of an alternative to a free-post bounty (but less sweaty and formal) or a challenge (but less sweaty and formal and crap), and we've been doing a few. I think @valerie_4659 originally started it, or maybe not (it's just where I saw it first), but in the end of the day that doesn't matter.
It works by tying posts together with a theme tag, and then pinging a few people you think might be interested so anyone knows about it, with the implicit (and possibly explicit) understanding that there's no pressure. It's all supposed to be as freewheeling as possible, so there shouldn't really be many rules. Want to feature a cool LoRA? Go ahead. Want to post your waifu? Sure. Want to do something completely unrelated? Well... maybe not, but feel free to start your own – unlike a bounty, it's free. This is not fishing for prizes (though everyone is free to tip, of course), it's supposed to be a chance to do something informal for the community, for fun. All you get out of it is a slightly elevated chance that anyone will look at your post, but oftentimes that's the hard part.
What to do
At minimum, just making a post with the hashtag. Note that this is about post hashtags, not image hashtags. Then optionally link a few people from a comment to that post, by username (we have found that doing it from the post description does not send a notification), and ask them to do the same – and maybe tell them that they are free to ignore it. Maybe also comment on other people's posts/images, they'll appreciate it. Basically, just engage with the event and you'll be fine. People have also been adding tags for "iterations" of the event, which you obviously are free to do. That made sense for a themed day, but I don't think it's really all that useful, these things don't move quickly and it doesn't really matter which round you're in when you're a week late anyway, and there's nothing saying you can do only one post per week.
If you want to start your own from scratch, I also recommend writing an article (as I am doing now), the point being that that sends a notification to your followers, who presumably care. Plus, I've found that post hashtags can be very hard to discover naturally, for everyone else. Explain what you're doing or (if you agree) copypaste these paragraphs, or just link here.
Most importantly... take it easy.