I agree with jc but the other thing that i do is that i put the wax ring on the toilet rather than the flange on the floor to avoid having it slip on the flange.
Toliet Wax Ring Dilemma
Two of my toilets have had trouble with flushing so I removed them to find out that the plastic ring inside the "wax ring" was crumpled and bent,which prevents waste from exiting to bottom of the toilet. Since most wax ring kits come with the black plastic cone attached, is this needed? Do I need to trim the cone before installing to toilet? Could the cone be getting smashed as the toilet is set? What can be done to fix this problem? 
