This is a very good question and as I handle all the recruiting for two of my games and I obviously run rpg_connect, I find I've become quite an expert at recruiting. It doesn't matter what the game is, generally speaking, the role-play community at this time is very circumspect of group sls in general. There's a lot of negativity going around so the real question becomes--how do you get around their initial reservations? You can post your ad in however many communities you want, but it doesn't guarantee that people will join. Some won't join unless you have pretty graphics and interesting codes and others refuse to join a game unless they know the mods or someone else in the game. Over the years I've developed quite the little black book of roleplayers so when I open a game, I reach out to them because word of mouth is probably the best form of recruitment out there.
Any good ad will have three things--a short and sweet description that briefly explains what your game is about, important links, and some sort of image. Not everyone is graphic or code savy but there are a lot of people out there that have those skills--so it won't be difficult to find help (you can even request that here as this community is here to help each other (I may even offer those services on my own community at some point if it's in demand).
Ads don't need to be posted every single day but make sure you read the community rules as many have a cap on how many times you can post the ad--I plan to put a tutorial together of all the current and active advertising communities with their basic rules for posting soon. Once a week is plenty if you're trying to generate new blood and i personally typically post my ads on Tuesdays and Saturdays to try and get as many people as possible.
Don't get me wrong there's no full proof plan and no right way to do it but I personally feel if you have networking connections definitely market those to friends and spread by word of mouth.