Begin with a clean face and no moisturizer. Facial hair will not stick to greasy skin.
Decide what kind of facial hair your character requires. If it's just a five o'clock shadow, use stippling and a stipple sponge instead of actual hair.
Choose whether the beard, mustache or other hair should be curly or straight. Crepe hair comes curly and will need to be steamed for a straighter look.
Apply spirit gum or liquid latex to the area of the face where hair will be applied. Work in one area at a time so spirit gum won't dry too quickly.
Position a small amount of hair at a time, especially when building a natural looking beard. You can always add more for a certain look.
Trim beard or other areas after the right amount of hair is applied until desired look is achieved. This includes eyebrows and side burns.
Remove beard carefully at the end of each performance to be used again. If it is made well, you should be able to use the same facial hair over and over.