I'm in China so generally there are guidelines for each place if you can get communication going. Some are written by you on the girls docket and add to your bill, and the girl will help by writing what she thinks she deserves
As to a regular? I tip well, very well if she is regular. For one if helps her clear her calender for me and meet at times she may not be on duty. But mostly because if she is a regular, its for a reasong that she goes beyond the usual effort/gfe/filthiness/rule-breaking/vaginal-clenching (delete or add as appropriate for a tip total). It is rarely about looks, all about attitude.
I recently gave a regular a tip-rise when I found out a younger and prettier girl in the same place was getting more for less skills and service. There's no way my regular deserves less. For context I've been going to her for over 7 years and she continues to get better consistantly. She has hinted more than once she would let me be her sponsor, which would be fun I cannot accept, but I do care she does well.