From what I can tell, NUBs always join the highest scored "open" clan at the time they are advised to join a clan in tutorial. So the only way for lower scored clans to get more people is to have the highest open clan score. I propose having Clan Descriptions and perhaps better organization in the "join a clan" screen. This way, clans can post minimum CP required so that players can choose a clan wisely. I know as a clan admin that I've kicked many people because their score is not high enough, which surely can be avoided if I had a clan description.
ie.
Shinobi Sanctuary is a very competitive clan. We expect excellent clan participation and score. We have a minimum of 1000 Clan Points per day. You must remain active or expect to be kicked. Absences must be notified to the clan.
Of course, for the NUB to understand what clan points are, the tutorial probably needs a couple more clear details about clans...
Just an idea ^^