i have worked with professional haunted houses for a long time, so i know how to really get people's heart racing. first, you need lots of hanging obstacles for the people to walkthrough, (bodybags, skeletons, etc.). it all depends on how much expense you want to go through. you absolutely NEED music, i would recommend the soundtracks from signs, X-files, exorcist, anything that fits well with your theme. you should keep to one theme. have scare-actors where people are most vulnerable (where there is fog, strobes, and dark would be the most vulnerable place.). have a lot of corners, and curves, it is also important to have a long corridor as well. if, you have it go through your house, be sure to use the garage and backyard.
NEVER POINT STROBES DIRECTLY AT THE PATRONS. strobes go well in a foggy area. use fans, to make it cold. when people get cold, they become more vulnerable. hang wires from the ceiling, so when the people walk through them, they feel like spider webs. blacklights are good in small amounts (unless you are doing a 3D maze).
here is a trick i learned a few years back. lay a row of PVC Pipes on the ground, and lay boards on the pipes. (be sure to have a handrail) when people walk on the platform, the floor shifts.
this place will be of a lot of help:
or if you are looking to pick up ideas from other people i would recommend this place: