I usually confirm the next appointment first (read all about scheduling in the Scheduling section).
“Great! Do you want to pay with cash, check or credit card today?”
If you plan to keep their credit card on file using something secure like Simple Practice/Stripe add:
“I’ll keep this credit card on file so we don’t have to run them each time and so it’s no big deal if you forget to bring it. It also covers you if you ever have to cancel last minute or don’t show up to an appointment.”