Formatting, formatting, formatting.

Easiest, and I can't stress enough, but the easiest way to generate some interest. You want to catch someone attention in seconds and having things clear to read and in paragraphs with colourful headings, dot points and a clear indication of what will be expected in the RP can improve your chances of people joining so easily. 

Best part of all is that it requires little effort. 

[url=http://www.roleplayerguild.com/topics/79554-01101001/ooc]One of my roleplays[/url]
When I created this roleplays the interest check went psycho with people wanting to enter. I only wanted two people but ended up asking for PM submission of character sheets to choose the best for what we needed. So we had it all set up even before starting the true RP, and I believe a lot of was due to the ease of relaying information.