In short, mix things up throughout the month. They can really help people feel more comfortable. Good marketing - Perception is reality. If the group is perceived as a good place to be, it will become that. Good marketing will attract people.
People like to belong to things.
Use clever titles to promote certain topics. Be creative, but tasteful. If you're a youth minister, hang out around high school and meet your youth group students there. Be on the lookout for young kids who might benefit from your group. Atmosphere - Create a comfortable, inviting, upbeat atmosphere.