how do you know when to mate

Question
I have a female pekinese who is 22 months old.  This is her 3rd heat and we would like to mate her.  How do I know the correct time to breed her?

Answer
Some breeders will breed their females day 13 and 15 (from the first day of bleeding).  

Each female ovulates differently.  But if you have a new male that you are using, introduce them around day 10.

A female will "flag" (move her tail to the side) and stand still for a male when she's ready to be bred.