A well-planned guest list: Think long and hard about who you want to invite to your party. Avoid inviting people who are known enemies—for instance, you probably don't want to invite both halves of a recently divorced couple, and the “frenemy” who always finds ways to criticize you or flirt with your lover should be skipped, as well. Invite guests early, up to a month in advance, then send reminders or make a few phone calls about a week before the party so you'll have a better idea of how many guests to expect. Be sure to put all the necessary information on your invitations—address, start and end times, what to wear, what to bring, etc. Also include a teaser to let your guests know what they can expect. A choice phrase such as, “Be ready for an evening of magic and mayhem,” will really get your party goers motivated and mobilized.
Plan for the slackers: Even if you've put on your invitations that guests should arrive in costume, be prepared for at least some of your guests to show up in their everyday street clothes. Instead of letting them parade around in plain fashions, have ready a box of random costume components. Wigs, hats, funny sunglasses, capes, make-up, and other accessories can be used to whip together a costume in a flash. If several guests arrive without costumes, you can even have a contest to see who can create a costume from the items you have on hand the quickest.
Encourage mingling: If you want your guests to mix and mingle, your best course of action is to get them moving. Set up different activities in different areas of your home: a spooky movie in one room, dance music in another room, food in a centralized area, and a fortune teller in yet another room. This set-up forces your guests to wander around in order to experience all your party offerings, and in doing so, they're likely to strike up conversations with the other party guests.
You still have plenty of time to get ready for your Halloween party, and with these tips in mind, you're ahead of the game already and well on your way to being crowned the supreme ruler of amazing parties!