Arc Lio Z.
For flossing: make sure you scrape both sides of the teeth with the floss. For brushing: don't be afraid to brush the gumline as well!
You have to reach all the way around with the floss and get all the nooks and crannies! I slow down when I get to my back teeth, I sometimes floss them twice, and oddly, it actually helps to close your mouth a little bit – your jaw joint relaxes and you can reach back farther.