Until there is no obstruction! For me, maybe twice each tooth, but if I’ve been eating beef or something I felt get stuck, then I will floss until it’s clear.
Twice, because the first time is to just do it, right? And the second time is to make sure there’s nothing still in there in between the teeth.
You should slide the floss back and forth with pressure against each tooth. You should also go as deep as you can. Try to get underneath the tooth even. When you first do this, there could be a little bleeding, but if you do it daily, this will stop. You will be left with clean teeth and even more importantly, healthy gums.