1) Chances are, if you're posting a full setting or a detailed idea, it's going to be fairly lengthy. So here's a general rule of thumb: If it's more than two paragraphs, put it behind a cut.
2) Also, if your plot/story idea is not work-safe (rated R or NC-17), it belongs behind a cut - with a warning stating that is carries a higher-than-PG-13 rating.
Note! For those that don't know, the code for an LJ-cut looks like this:
<lj-cut text="Whatever you want the cut link to say.">
Whatever text you want to put behind the cut.
3) Posting an idea here means you have no problem with someone else using it... however they wish. If you don't want to take the chance that someone's going to take your Family of Kitties Christmas Story plot and turn it into Christmas Catgirls Craving Childflesh, then don't post it. Someone may take the entire idea, several aspects, or just the barest hint of what you put here.
4) Please keep your posts limited to your ideas for plots, settings, and such. There are many other lovely communities in which you can post your writings. If your idea is actually a couple paragraphs or the start of a story you aren't continuing, that's perfectly okay. Posting up what you've done with an idea you've found here is not, be it a poem, story, or RP.
5) If you've got a bunny attached to you that thinks Jayne and Simon from Firefly should run away together and get married, you are welcome to post it here. However, please keep in mind that other members may not do anything with this idea. Even if they do, things may be changed and it might not be what you want/expect. (See #3.) We don't do fic challenges here. There are many, many other, fandom-specific communities that can and will cater to that. plot_hooks is primarily geared towards original fiction.
6) Come across a link that provides writing prompts and pick-me-ups? Post away! Likewise, finding a site that has anything that might be of interest to a writer is welcome here - a site that explains why character development might be approached, or how to keep from writing yourself into a corner, for example.
7) Tags! Tags are loverly things. Please take the fullest advantage of them. (I am not grinning lecherously. I swear. Okay, maybe a little.) Your post should be tagged with the genre(s) that fit your idea, as well as either 'rpg', 'fiction', or 'fanfiction'. If more than one category is appropriate, then go ahead and use more than one. Less is not more in this case. If your post contains a link to a writing resource, please tag it 'resources'. Any posts made by the maintainers carries a 'moddish' tag. This makes things easier to find for anyone looking for something specific.
8) The maintainers enjoy Coke and anime, should you feel the need to give us presents. Furthermore, giving us presents is encouraged.
You forget to put a long post under a cut, or the HTML happens to get typoed, and now there's a page and a half of your best R-rated story idea floating free. Don't stress too much over it, it happens.
If a post doesn't meet the rules, we'll leave you a comment asking you nicely to edit it and telling you why. Then we'll leave you alone for a piece to do so. If it doesn't get edited within a reasonable amount of time, your post will be deleted.
We also have a three-strike rule here. If we have to delete three of your posts, you will lose posting privileges.
Cause trouble out of hand, and we'll just flat-out ban you. =^.^= And be happy while firing up that admin console for a ban_set.
I think that's about it. Questions? Comments? Stuffed penguins? You can comment here or email firstname.lastname@example.org.