Hire a Pet Sitter
If everyone has plans outside of the house, sometimes there is no choice but to leave your dog home alone. When bringing your dog out and about this Halloween, make sure the environment is stress-free (take into account sights, sounds, unfamiliar people). Otherwise, it may be wise to hire a local sitter who watches pets, or ask a friend/neighbor. Crimes and cruelty against pets is very common on Halloween, especially for black cats and dogs. So make sure they are not left in the yard where they can become very easy targets. Knowing there is someone there for your buddy while you are away is always a good feeling!
Keep Pets Away From The Door
Trick-or-treaters come and go, and your door continues to open and close, but keep tabs on your pet! This situation allows them to bolt outside while you are distracted. It is possible they could get excited by another dog, or the high voices of children. Also of note is that kids may have allergies, so going the extra mile to confine your pet away from the door guarantees that everyone is safe.
Probably obvious, but worth stating. Do NOT feed your pet any candy, especially chocolate. Keep an eye on kids potentially giving any candy to your dog as well. However, sometimes dogs find a way to eat what they shouldn't. In case of the worst, call or visit your vet immediately, and watch out for signs of chocolate poisoning such as vomiting, diarrhea, rapid breathing, or seizures.
Make Sure Candles and Electric Cords Are Out of Reach
For candles - a pet could burn themselves or knock them over. And cords have the potential to be chewed on. Determine the best layout for decorations out of the way where a pet cannot reach.
Double Check Your Pet's Costume
Be certain that your dog will be comfortable wearing a costume. Have them try it on before the big night to determine if any skin issues or allergies turn up. The costume should not be too tight, or have loose / dangling strings or tags that could be chewed or choked on. If everything checks out - your dog is ready to show off their style!
These are only guidelines for assuring that your pet will have a safe & happy Halloween.
Also of note is for cats in particular - if possible keep any outdoor kitties inside a few days before and after the holiday. Notably black cats are sadly stolen or killed around Halloween and the month of October. Always make sure your pet is safe & secure.