I don't think I could ever be a serial killer, as I prefer to use my stalking and stabbing talents for good instead of evil, but the original film "Friday the 13th" provides what appears to be a deceptively easy guide for getting the job done. Watching this film--released in 1980, when people were so full of Carter-era malaise that able-bodied young adults had to work at a slum of a camp just to make ends meet--makes you think that even SPOILER ALERT! a slightly built middle aged woman could successfully murder seven able-bodied young men and women in one night using basic campsite implements.
The story is the usual American dream--woman works as a cook at a summer camp, her son drowns because he's an idiot and the counselors are basically too busy having sex to do the jobs that they're barely paid to do, and the woman goes crazy and hears voices telling her to kill all counselors because this makes sense. You can even hear her saying to herself "kill them, Mommy!" rather than "hey maybe this isn't the most healthy coping mechanism, Mommy!" as she stalks her final victim. The fact that the killer looks a bit like Helen Reddy also makes her able to get the jump on unsuspecting idiots.
Now, why do I refer to all these murder victims as idiots? Let's start with the fact that the camp has an arsenal that would make Charlton Heston proud, and yet once it becomes clear there's some murderin' afoot, that's not the first place the victims go to arm themselves to a tee and go all Republican all over the place. The killer, meanwhile, uses arrows, a machete, and an axe to calmly dispatch each counselor, one by one. (Somehow, Helen Reddy must have gotten Green Beret training, because this film clearly inspired the Rambo "First Blood" film that came out two years later).
Also, the woefully unarmed counselors manage the split up constantly, giving the killer a chance to isolate and gruesomely murder each of them one by one. When the twist develops and you see the killer is just Helen Reddy, it makes you wonder why none of the victims (until the last one, of course) tries to even fight her when they see her. Yes, if you're being impaled with an arrow from under the bed you're laying on you don't have a chance--but many of the victims see the killer and just stand there screaming. Hey, if you're going to get chased through the woods by a woman with a machete, huck a rock at her! Make it sporting. Helen Reddy is woman, hear her roar, as the rock clocks her crazy-train skull!
The film of course spawned about a hundred sequels, each of which is worse than the last, lacking suspense or even the humor they were going for--and based on the idea that the "dead son" isn't really dead and is now out avenging Helen Reddy's death which then means the entire premise is based on a misunderstanding of "Three's Company"-level proportions. But there's another issue easily overlooked here.
Helen Reddy has been murdering counsellors twenty years after her son's death (or presumed death, according to the sequels). Did it not occur to her that any summer camp in New Jersey would need liability insurance, and she could have sued them for wrongful death and lived a very happy life, maybe even having another son who knows better than to go in a lake when he can't swim? Then the movie could have been called "Friday the 13th--Living Large!"