As i replied in another thread, sweep instances for frags of ninja you want to use now or in the future. Check what characters get skillbooks, if you want some of them then sweep their instances. If you don't want any of other ninjas, just sweep the 10p ones you have at 5* or you are close to get to 5*, so u can get more frags for refining. You will get all of the elite instance ninjas over time (some will take really long, like deidara/tobi/ningendo) from chases, survival trial or black market. Same rule applies to shops- get ninja frags of ninjas you want to have. If you already did that or dont want any of them, get 5* ninja frags for refining.