Step 1: Planning!
After you pick the room you'll need to estimate how much supplies you'll need to cover it. Most importantly, how many piece of furniture are in that particular room.
For example, I used my living room as the main "killing" room. Which has 6 pieces of furniture I would need to cover with white sheets.
Step 2: Supplies!
1 White sheet, blanket, or piece of fabric per piece of furniture.
1 White table cloth per table.
Plastic Sheeting (I bought the 600 sq ft pack and it was more than enough. You could opt for a smaller amount for sure. I got a big box because we are also painting soon!)
Large black garbage bags.
Some fake plastic human limbs.
Photos of some of the guests, if not all attending your party.
Various knifes, a hammer, a hand saw, any other tools you think might add to the creepy vibe!
Staple gun or stapler, with lots of staples!
A friend to lend a hand.
Note: Be thrifty! I was able to find all my white sheets at a local goodwill for about a dollar a piece. For the table cloths, I just went to party city and got cheap plastic ones.