Make a plan:
It seems so simple, but a good host has a plan. Last minute miscommunications or misunderstandings about your event will stress you and your guests out. Make sure you know everyone knows exactly what is expected of them, simple things are easy to miss like: where to park, or that they were expected to bring cookies only instead of cheesecake.

Create an invitation list:
Who do you plan to invite? Your office, neighborhood? Adults only? Make your list first. Be realistic about how many people you actually want to accomodate, and keep in mind many people feel busy and overwhelmed during the holidays and may decline.

Create a group:
Create a group on your platform of choice. WhatsApp and Facebook are popular options. I love WhatsApp for inviting friends to events because we can all converse easily and get excited when we see what other people are contributing. Keep the event open until after the party is over so you can share photos and recipes.

Ask your invitees to determine their contribution + ask them to bring their recipe for sharing.
Create a sign up sheet - one of the most important parts of a cookie party it making sure everyone gets to bake and try different, create a first come first serve list and ask your guests to stick to it.

Be inclusive: Not everyone likes to bake, but they may still want to participate. If a friend really doesn't want to bake, ask them to bring a store bought savory dish to snack on while you exchange cookies. Unfortunately, too many friends who won't bake will mean there aren't enough cookies to go around. So encourage your friends to step out of their comfort zone and try something new!

Be clear on expectations:
Be sure to ask guests to bring cookies only. Cakes and cupcake are harder to transport and I like this boundary because it really allows everyone to try a new cookie.