Brovo said Interest Checks

One of the rules of advertisement: If it can't be understood in five minutes or less, nobody will be interested. Post an excerpt of the plot you want to run, no more than three paragraphs, and then devote one paragraph to just explaining clear as day what you want and what the RP will be about. For example: You have a fantasy RP? Try having the King of whatever nation write a letter to another, detailing the main conflict at hand for the party, add some exciting words, words that are vague enough to conjure any image but powerful enough to convey the validity of the problem at hand. Think words like: Cataclysm, apocalypse, endless, brink, destruction, terror, etc.

After that, keep the interest check afloat. Answer everyone who comes in. I mean everyone, even a simple "I'm interested", reply with a thank you and a smile. Even if half of them don't show, if you get the interest of like, 30 people, that's still a solid 15 who will arrive to join the frey.

OOC structure

Comes in a variety of valid ways. If you're going pure text, always put the plot up front and centre as the first portion, the character sheet second, and any information thereafter third. If you're in casual, keep it below 2,500 words. If you're in advanced, below 6,000. Nothing drives players away like an OOC that takes a solid two hours to read and understand.

And, again, keep excitement alive in the initial phase. Respond when you can, use teasers, answer questions. The formatting of the OOC just needs to be solid enough to garner attention--what will really keep people keen is in how well you can keep the tension going for whatever is going on.

Brovo said
Hm. Time to expand. :3

Well the king's letter example is what the literary world calls a hook. The movie industry calls it a trailer. Video games call it a teaser or demo reel. It's the very first thing people get to see about the universe.

The best way to show your players your world is, well, showing them, not telling them. Saying "my world is a fantasy RP involving the kingdom of Tyr" is information. It's telling the person what it is. Showing an excerpt of how the characters behave, followed up with the OOC explaining what they just witnessed and explaining what they'll do, is showing them the world and then using information to explain it. It yanks at someone and says "HEY! LOOK AT ME! I AM IMMERSIVE! MY WORLD IS ALIVE AND ASKING FOR YOUR HELP!" Instead of, say... "The world of Tyr is in danger by the evil monster."

Using that method I've never had an interest check fail. LoR 2's interest check was apparently so wildly successful it blew away all expectations and garnered over 30 players into my OOC initially. Take that for what you will.

EDIT

tl;dr: Marketing tactics 101. People prefer to feel involved directly, as though witnessing something or being spoken towards, instead of being informed in a wiki-like fashion. Why? I have no idea. Go ask a psychologist.