If you want more members, invite your watchers and the people that you watch, works well. (and you get members pretty quickly. works with my group anyways.) an other thing, try to make you home page a bit more flashy and eye catching. add more pictures, emotion icons... those kind of things. you can also check out:
plzcatalog.deviantart.com/ [for decorations]
art-paws.deviantart.com/ [my group for an idea of how to decorate and where]
all-deviantarts-art.deviantart… [pretty much the same thing]
art-zone.deviantart.com/ [more ideas]
hope it help ^-^