When planning your haunted house, sometimes where is not important as when. I mentioned in the Narrative section that the best haunted houses have a story. Everyone knows (or should know) about story arcs, most wonderfully explained at the link. The idea is that you build tension until the climax, and then release it through the denouement. Admittedly, with a haunted house the relief comes from leaving, but the relief is there all the same.
So it's very important that you don't start off with your biggest scare. Sure, the Devil rising from the depths of Hell, screaming legions of the damned clutched in his talons and fire spouting from his mouth is cool, but what do you do for an encore? There's a reason Dante's Inferno starts at the outside and works in toward the image of Satan, and it isn't theological.
You have to build to your greatest scare. Sometimes this is simple: figure out what your scariest thing is and put it last. Find your not-so-scary things and put them early.
If you can, get your guests dreading your later scares. If you will be chasing them out of the house with a chainsaw-wielding maniac, have copious amounts of fake blood and fragments of newspaper stories around. ("Mysterious Slaying At Cabin!" and the like.) If vampires are your thing, strands of garlic and Gothic crucifixes are good for the decor. But whatever you do, build. A blood-drained corpse is scarier before you meet the monster who drained it; afterward it is not warning but verification.
Another important trick is the "big reveal." A monster that jumps out at someone is better than one waiting at the end of the hall for them to draw near. Place something scary or shocking just around a corner so a guest turns and is suddenly confronted with something horrible.
Position your scares appropriately and you'll make your house a thriller.
Next up: Scenarios!