I grade the teeth. First 8 up front get $1, Eye teeth are $2, and molars are $3. If there is a cavity or a filling in the tooth, the amount is cut in half. If the tooth is knocked out (traumatic accident to a tooth that was not loose) or pulled by the dentist (not loose), the amount is doubled.
I also like to leave encouraging notes from the tooth fairy (written with my opposite hand to disguise my handwriting) that say things like: "Keep brushing; you're doing a good job!" or "Needs a little work; let's keep those pearlies white."
I hope this helps. :o)
P.S. Find out from your little ones if their tooth fairy is a girl or a boy. When I was growing up, I simply "understood" that the tooth fairy was a girl because that is what I was taught. But, according to my older son from when he lost his first teeth at age 3 (traumatic accident that knocked 2 of them out: that blow cost me $4), his tooth fairy is a boy.