We recommend starting to promote your FPU group 6-8 weeks out from the first meeting. That may feel like a long time, but remember some people can't attend church or your small group every week. Also, remember repetition is important as well. It is a known fact that people don't typically respond to something until they've seen it at least 7 times...marketing calls this the "rule of 7"!
Our Promotional resources page contains everything needed to make the group successful.