The AVMA (American Veterinary Medicine Association) shared 7 tips for keeping your pets safe on Halloween. Among these: don't give your pets candy (and keep it out of their reach!) This especially includes chocolate and candies containing xylitol. If you are going to dress your pet in a costume, make sure it doesn't interfere with the pet's ability to breath, move, or open its mouth, and that it doesn't have any parts that can be chewed off.
For the dogs and cats that aren't thrilled about the doorbell being rung or strangers stopping by, provide a quiet place away from the hubbub where they can hide.