I hope I dont re-post any ideas already up as go- but the easy way to go is the old "haunted house" theme, dont clean your house, mess it up more. buy that caution tape to tape out any areas you dont want guests to go. cover furniture in shower curtains or plastic tarp then old white sheets or any light color will do, and they can have stains and holes- ask neighbors, everyone has a linen closet of shame, even if they are just loaner sheets. change out all your white bulbs for either a color like orange, or the black ones (but dont use black where the food is out, it can make food look too unappealing) you want your rooms to be slightly dim but not too dark that people have a hard time getting around. but lighting works well to mask sparse decorations.
do decorate your bathroom the guests use. I always have one orange bulb in a night light in there but the lights turn on to a 40 wt dimmer but not too dim regular light- you want your guest to be able to aim well but not adjust their eyes to very bright light before they come back out. you can paint on your mirror, fun warnings or even spooky eyes watching you. it cleans off when your done.
dont forget fun Halloween music, look for a good CD mix.
if your in to the lame games, we have put up a large poster sized drawing of a witch with huge nose, then blind fold people, turn them around and have them bite the end off a gum drop candy (those chewy things covered in sugar) the stick the sticky exposed side to the poster and the winner is he who gets the wart in the best place (usually the tip of the nose)
we did a peanut push race, but you had to push a rolling eye ball across the floor, tho its hard when your in a very elaborate costume.
costume contest is more fun if you make people line up, and each person has to act out their costume too, do this after everyone has dipped in the punch bowl a bit, it adds some entertaining fun to the voting.
if you have some old clothing ( or can get some) put out a box for anyone who dares come in street clothing, let the other guests dress them! old table cloths are funny capes, and if you cut a hole in the top, they make a costume right there. next year, everyone will be in costume, cept the newbies.... AKA, your new victims.
put out lots of fun foods, and do add to your invite to "bring your favorite Halloween dish" everyone has some fun idea. but you should put out the punch and some small sandwiches for later to help people get ready for closing time
good luck.