I am going to make a real life horror aventure with friends! need help for scares!

[Leu Radu]

Dang! I wish I could be there to help you out physically. I love this kind of stuff!

As GraphicsKid said, start slow and intensify it as the night goes on. It's all about creating atmosphere, making it tense, and then giving them a shocker. Depending on how much it's going to take, you can make large pauses between scares (too often will blow your cover, and that's the last thing you want).

A few direct suggestions:
-Think a little about what scares the guys and try to use it. Maybe they're afraid of insects? muhahaha >
-Make your friends tell some horror stories. They shouldn't focus on "fantasy" stories, but something that they can relate to ("my dad once told me a story about a friend of his...","A cousin of mine died in a place like this...", "did you hear that in this neighborhood, ..." stuff like that). I can pm you a few stories if you'd like.
-The noises that you make should also have some kind of natural explanation ("Is it a rat, or a bird, is there something else in the attic?")
-You might move objects around a bit so they seem to be something else in the darkness. Consider the way they enter a room or hall: if there is light shining from a place, try obstructing it with a strangely shaped object. Also, dark corners should have some suggestive objects that would get their imagination going. Try to make as many hidden spots as possible (and empty space behind a piece of furniture, a corner you can't easily reach because of debris), they can also stimulate imagination (and who knows, maybe they can be a good hiding spot for you).
-Mirrors! It would be really cool if they could scare themselves with mirrors.
-Don't set the scene too obvious. If they see, for example, that you made a vase fall with a piece of string, they'll probably know what to expect next. Try something more ingenious (simply placing objects in strange places, on the floor, or on the staircase, might make them stumble upon them). You might as well tell your friend to "accidentally" do something.
-Dismiss anything macabre. Fake blood or body parts will only make them realize the scene is set. Oh course, if you can procure the real stuff... muhahaha >
-You might put something that will tell them somebody has been there not long ago (an empty/half empty bottle, a wrapper, a tin can etc.). Even the idea of having a homeless somewhere hidden in the darkness is scary, isn't it?
-Make sure you do not blow your cover before the final scare. It might take quite a lot of stealth and patience, but I'm sure you can do it.
-You could tell one of them to "play" the explorer, so he could take guys to different part of the house because he is supposedly curious. If he goes alone, he might disappear for a while.

I hope this suggestions will come in handy in some way. Good luck! I'm really curious how this will turn out.