If you are fisting multiple persons, make sure you change gloves every time you change people. Be also very aware some woman have allergies to latex and silicates and like all allergies this may be life threatening in some cases. Use a good quality waterbased gel, lube, with no additives, flavour or colouring agent. Because the anus has no self lubricating mechanism, use plenty of lube making sure the glove is well covered and there are no dry patches. The same of course applies to fisting of the vagina, one cannot have enough lube.
Some women have reactions to certain brands of lube.
If she complains of burning immediately withdraw and flush the vagina with a soft water douche. Remember if a douche has been used to allow the vagina to return naturally to its natural lubricated state before penetration of with the penis.