The useful first step at San Francisco International Airport is to treat the airport's own transportation page as the source of truth. After baggage claim, follow current rental-car signs and keep the destination---SFO AirTrain Blue Line to the Rental Car Center---in view rather than navigating to an unrelated public address.
At SFO, follow airport signs to the AirTrain and verify the Blue Line connection to the Rental Car Center. Use SFO's current transportation guidance for terminal changes, return routing, and accessibility information.
Before leaving the facility, confirm the agency's current hours, identification and payment requirements, vehicle notes, and return instructions. Photograph the vehicle condition and keep the official airport and agency pages available for the trip home.