It depends on how much respect you have for the individual. The proper way it to make the prosthetic on a life cast or even a partial life cast of a part of the face to be made up. The area is covered with alginate and then backed by plaster or plasterbandages and removed. Then the mold is poured with plaster. This "plug" is the replica to the part or whole face to make masks or appliances upon. Some kind of release agent and then your latex mixtures and so on.
You can if the person is not alergic to latex (pretesting a spot before proceeding) you can apply directly to the skin but over an eye or mouth should be done off the subject and applied with spirit gum.
If you have no reguard for the individual at all, simply use latex and kleenex to cast over the eyes and mouth, nose holes and ear holes directly and spin them around a few times and leave. Chances are there will be a lot of flayling when you get the mouth and nose covered and it might require an assistant. Of course this is how so many get caught, having a witness.
Another fabulous post from the U.S.Department of Wild Imaginings, now in spectaclar stereo, sponsored by the Adhesives and Sealants Council, suggesting ways to stick things together since the 1800s. Not fabulous in a gay way. Your results may vary. Illinois residents add 8% sales tax. These posts have been made by professional post makers, do not try this type of posting on your own without extensive training, lovely assistants and a trusty clown horn.