The majority of pickers will rest either the ring, pincky, or both on the head lightly for a reference in hand positioning.
Best practice is to experiment and decide what is most comfortable and useful to YOU.
There is no exact way to do this "correctly. If you study hand positions of different great players you will see they very slightly form one to the other. Some, JD Crowe for example, have even altered their hand positioning, and even the spacing between the strings, that they use over the years.
It is about what best suits you and the way you are wired. We are all individuals and different when it domes to coordination, dexterity, an what is comfortable for us.
Best of luck with your banjo journey!