If you've read every book twice (or more); if you wear shirts with phrases like Bite Me and Only a Vampire Can Love You Forever; if you've already pre-ordered your Twilight DVD and plan on watching it the second you get back home from buying it in the wee hours of the morning, then throwing a no-holds-barred Twilight release party is definitely for you.
Gather some fellow Twi-hards together and let it all hang out with some Twilight inspired decorations, games, food, and fun.
Invitations

Every good hostess knows that a great party begins with great invitations (just think: W.W.A.D.? What Would Alice Do?)
You can't go wrong by presenting each invitee with a red apple tied around its stem with a red satin ribbon. Attach a tag on the ribbon with the formal invite and party information printed in, what else?, the font used on the cover of the Twilight books. The font is called Zephyr and can be downloaded free here.
You could also tie the invitations with red satin ribbon to red and white ruffled parrot tulips (a la New Moon), to oversized chess pieces (you can purchase oversized white queens here), or simply scan/copy pictures of your favorite Twilight characters onto cardstock and use as the cover of the invitations.
Decorations
Again, take a hint from Alice Cullen: pay close attention to detail and get as extravagant as you possibly can without being forced to declare bankruptcy.
Outside the front door: First impressions can go a long way to making the evening festive, so try to set the scene for your guests before they even enter the party zone. If you've got twinkly white lights, now is the time to use them; hang them everywhere in front of the house. Even better, if you've got some fake Christmas trees, set them up right outside the front door and hang lavishly with lights.
You might want to hang a sign on the door to alert party goers that they are now entering Forks: something like Welcome to Forks with one arrow labelled Werewolves pointing to the left and another arrow labelled Vampires pointing to the right would get a laugh.
In the main party room: Your job here as hostess is to create an appropriately Twilight atmosphere. Start off with more twinkly lights, both red and white, hung everywhere. To make a misty sort of Forks-y feel, tack white or gray tulle fabric from the ceiling and, for the ultimate Forks touch, have a fog machine going. Fake trees, especially Christmas trees, would make for a nice oh-no-we're-in-the-woods-now ambience as well.
Everywhere around the room, put as many Twilight-themed decorations as possible: display the books prominently; hang Twilight movie posters hither and thither; placed framed photos of the characters and of the Cullen family crest on tables and shelves; set bowls of red apples, vases of red and white parrot tulips or fire and ice roses, and oversized chess pieces everywhere you look; fill jars with red, white, or black candy.

And while you're at it, why not invite Edward and Bella themselves? Amazon sells life-size stand ups of the star-crossed lovers as well as ones of James and Victoria here. Just think of the possiblities for racy little photos these stand ups present....!
The table: Vampires may not need to eat but you and your party-goers definitely will. Make sure the table is as lavishly Twilight decorated as the rest of the room.
Try using a red tablecloth with black netting laid over it (or vice versa); use items from the book covers (apples, tulips, chesspieces) as place cards with name tags attached. Place black napkins tied with red satin ribbons at each place setting, and use a smorgasbord of Twilight related objects as centerpieces, from the ubiquitous apples, chess pieces, and flowers, to blood-drip candles (you can purchase the candles here, or find out how to make your own here).
Don't forget the twinkly white lights! Alice would be proud.
Ready for more Twilight party ideas? Next up: Twilight themed party food for humans, vampires, and werewolves.