Disclaimer: The below is based solely on the conventions of horror, it’s just a facetious bit of fun.
Birth: Birth should be a traumatic time for you. You should probably be separated from your birth parents and adopted into some kind or hostile repugnant family of low intelligence. Failing this you could also be one of twins, separated at birth, you be the evil one with no love and no family with a life grudge against the good one, most likely a successful graduate and hunky doctor. Then there’s the family option. You stay with your birth family who just happen to be an abusive bunch of assholes who make your life hell from day one. They will pay for this one day! The easiest option of all is to just be physically deformed somehow from birth, this will get you well on your way.
The early years: This is the time to ensure you’re generally mistreated and picked on by siblings and piers alike. School is the perfect place for you to begin life as the outcast or weirdo (this will all add to your mystique later in life). You should probably start your hobby in dead things like road kill. It’s key that during these tender years you build up a lot of resentment to those who suppress you, such as your father, the law, school bullies, your teachers etc. It may also be important at this stage to find that one person who empathises with you, a school doctor, the pretty girl next door, your mother, a kindly neighbour etc. They will come into their own later.
The teenage years: The early teens should be spent much as the younger years but to an exaggerated level. At this point you should be on the edge. Now is the time to reveal the dark side of your personality, you’ll probably need to start a particularly bad fight in school. Your later teen years are time for the big disappearance. You need to get out of the public’s glare, either by state incarceration (prison or asylum) or by plain old AWOL. This is a time to lay-low. You’ll need to train hard (cardio and weights), plan your re-emergence, design your look (you’re going to need some kind of costume you know), become a skilled electrician (those lights won’t turn themselves off), and hone your skills with your weapon of choice. If you’ve stayed at home all these years then you should at least be living alone, either on the fringes of your community or in the family home where only you live now. The point is be elusive, you must become a bit of a local talking point.
The early adulthood years: Just like Leslie Vernon you now have two big decisions to make that will shape the rest of your career. 1) The object of your love, hate, and obsession (aka Final Girl). It helps if this person is linked to your childhood (sibling, or perhaps that understanding friend from home). 2) Find your nemesis (look here for clarity) perhaps that understanding doctor or teacher. Now it’s time to re-emerge into the community and sow those seeds of your return amongst the local teens. To do this you’ll need to let some teens have a narrow escape. It also helps to make fleeting appearances at mass gatherings (like parties) only to disappear again. You should also ensure your nemesis gets wind of your return. This should also be the time of your first successful massacre. Remember to ensure your nemesis and final girl meet. Try to leave them both alive by the end of it all. Most importantly disappear with the illusion, at least, that you are unharmed, and certainly not dead.
The glory years: Now is the time for repeat offences. Annual massacres seem to work well, you can even tie it in with a public holiday if you like. I don’t think Presidents Day has been taken yet? This is the time to repeatedly re-torment both final girl and nemesis. As well as letting out a trickle of new information about your past. You don’t want to become old news in the eyes of the media. You should know all the tricks of the trade by now; such as piling all the bodies up in your finale location for the final girl to find or how to cut all phone lines and electricity supply. Above all ensure that after each appearance you get the hell out of there. The biggest embarrassment of all to the fraternity is capture. That’s a big no-no.
The twilight years: Chances are you’ve seen off your original final girl and are probably down to some fairly tenuous family or childhood ties. Things will get a bit stale. So it’s time to freshen things up! You could fake your death and the return as the apparent walking dead, that’s a good one. Or how about finding another serial killer and taking them on. If all else fails you can try out the whole ‘in space’ thing but that’s just a bit Star Trek if you ask me. Never forget, in this line of work, there is no retiring, just longer gaps between appearances. Perhaps every five years or so? This is the time to take up other interests too, such as walking, climbing, fishing or gardening. Just make sure you keep your head down.
For further reading check out Behind The Mask: The Rise of Leslie Vernon (2006), Dir Scott Glosserman