You can easily attract RPers if you have all the information lay out for them. Here's some guidelines to the minimum of what you need on your post.

Your first post...
The subject should be your RP's name.
Then in the post, you should have at least the following items:
Name: (name of RP)
Availability: (Open or Close? Private or public? If you're looking for certain types of RPers, how many slots are open?)
Story: (The big parts! Describe the setting(place, time, era, etc). Then describe what's happening which characters will be involved in. Add any other information you'd like everyone to know regarding to the story)
Rules: (Finally... Very important! Without this, guild Crew won't be able to say much if someone does something you don't like and it's not mentioned anywhere in the rule. You'll have to deal with the problem maker one way or the other).

Your second post should be in depth information on anything you mentioned in your storyline that generally, isn't known on a general basis. For example; If I mentioned Exathrians is a half human half tiger race, I should be describing the Exathrians entirely in my second post. Another example; If I mentioned a certain city(town, village) that the RP will be taking place at, please describe the town at least at the basic level. If the town large or small, say so. If the town is peaceful, no one should be able to find a weapon shop and get an AK47, mention it.

Your third post (if you wish to come this far) should be a list of people who you've accepted or has joined your RP. If you have a character sheet thread made, you should link it here. You are welcome to use your third post as your character sheet collection at your discretion.