I've read more than a few slasher flicks lately and most of them have unfortunately been crap. I enjoy a good horror film as much as the next guy, but the problem with a lot of horror specs is that they get so formulaic when they involve a slasher killer. Here are a few of the more common tropes that pop up in the first acts of the weaker, more generic specs.
A disposable kill to start the film - Usually the writers in question are sharp enough to know that a good horror film has to start with a bang. The problem is that this early kill - which serves the purpose of establishing for the audience that there's a madman on the loose - rarely exhibits much imagination on the part of the writer. Most of the time it involves a cannon fodder character wandering around in the film's main setting. (For example: If we're dealing with one of those films where the killer stalks a bunch of campers in the woods, then the first scene has our walking target walking through the woods before getting killed.)
The most common mistake made in amateur scripts is that usually this victim has little to no connection to any of the other characters, and in bad scripts, this death isn't integral to the plot at all. It's just there to tell the audience "Killer on the loose." It's always better if you can make this scene motivate the story, and somehow set the plot into motion. For instance, Scream avoids this problem by using Drew Barrymore's murder as the catalyst for the police questioning everyone at school, establishing how Drew's character and her boyfriend are connected to the main cast, and setting up the motif of the killer. (In bad scripts, the slasher merely jumps out of the shadows and kills.)
20 pages of boredom - The hack writer assumes that since they've spent the first 5 pages setting up the killer, that they can spend the next 20 pages slowly introducing their large cast of characters as they go about their mundane lives before setting up the next kill around page 30. The worst script I read recently had one group of four teens killed while skinny dipping on the first ten pages. Then they introduced another group of six teens heading out for another camping trip. This involved five pages of the teens assembling for their trip. Ten pages of them on their road trip, which mostly consisted of smoking pot and arguing over pop culture, and then ten pages of them setting up camp - seven of which were preoccupied with the girls stripping down and skinny-dipping.
How much of that turned out to be essential to the story? None. Zero. Zilch. The only point that had any significance was that Prude Girl hadn't yet slept with Nice Guy and that neither of them were sure it was a good idea to do it on this trip. Naturally Slutty Girl and Tool Guy were advocating this hookup, while Soon-to-be-Topless Girl and Dead Guy #1 (spoiler alert) don't understand why they just didn't do it in the Jeep on the way out to the woods.
I know... I'm bored too. Just imagine twenty pages of this drivel.
Anyway, my point is that the movie could have just as easily started with Dead Guy #1's death rather than Anonymous Cannon Fodder's death and the impact on the script would have been zero, save for the fact that it would now be twenty pages shorter.
So take this lesson. Act One's are not the place to kill time. The story starts on p. 1 - not on p. 30