8g to 6g was my first time i taped my septum. prior to taping i would play with my ring excessively, i would tug and twist on it pretty hard and such, this occurred for at least a week or two,it loosened it up very slightly.
with this very slight loosening i wrapped on a very small amount of tape(compared to wat i would for ears) and on a ring, and i would put the ring halfway into my septum, and when it got to the taped part, i would tug down slightly to create a small gap so the tape could fit through. this was done at night. next morning when i went to apply the same amount of tape to my ring i noticed it was roughly the size of the 6g, so i tried inserting the 6g ring, and it slipped right in :)