How to watch (and why people say it wasn't scary)
First off, if you haven't watched the movie yet, there are no spoilers in this post. In fact, I suggest you read this post first before watching the movie and then follow the advice.
I keep seeing how people keep going off on how this movie wan't scary or wasn't any good. Then I see most of them saw it in theaters. Do NOT watch this movie with other people. Watch it alone, and in the dark.
This type of horror movie involves massive ammounts of suspense. If you have even the slightest distraction, you will lose it and the movie will just feel boring to you. This is probably the main problem people had with the movie the first time they watched it.
From what I have seen, any superstitious belief or any belief in the supernatural will greatly improve your viewing experience. If you even have the slightest belief that it can happen, it will feel much scarier.
The acting is also different than a standard "run of the mill" movie. By different I mean that it is actually much more realistic. Just go back over old home videos you have taken and see how your family members act on camera when they know they are being recorded and then when the fact the camera is on doesn't matter anymore.
If you want to get the full effect from the movie, here is what you should do:
1. Watch alone, in the dark, and don't do anything while watching (even eating).
2. Have some belief beyond the physical, doesn't really matter what. Even if you don't believe in demons the movie will feed off the slightest doubts you have.
3. If you have problems focusing on movies, watch another one before Paranormal Activity that is short and very action packed. May not work for you, but I find it helps.
4. Don't take your eyes off the screen, watch intensely. May wear your out, but it is worth it.
5. If you have already seen it before, watch 2 and 3 alone and in the dark, as going back and watching 1 again won't make it scarier or better.
And if you are wondering, it wasn't my favorite movie and I don't think it was as amazing as some people say, but I still had to sleep with the lights on that night. (Watched it alone, in the dark, at midnight, on Halloween.)