Well, you can always cheat, like I did, and not actually seek Permission until you've been writing for a year, and then have fifty missions count as your writing sample. But that's not recommended.

This is my first official request for permission. I intend to only use one agent, until I can get into one 'fic that really, really needs killing, if that's alright.
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I, HonuWahine, also known as IronAmerica, do hereby request official permission to become an agent or two of the Protectors of the Plot Continuum. I do solemnly swear to not kill a Mary-Sue until I have gathered sufficient damning evidence and/or facts as to their insidious nature and have a charge list of crimes against the Continuum and have charged said individual.
I swear that should I lose what sanity I have remaining within my grasp; I shall not pick up the nearest sharp/blunt/very dangerous/potentially lethal object and go running through the corridors screaming “Mr. Rogers!” I will also not wreak havoc upon my immediate superior and/or the Sunflower official and/or his associates. I shall do my best not to succumb to the level of a Mary-Sue when faced with a lust object or a favorite—no matter what memory altering device I may have in my possession. It never helps.
I shall uphold the well-being of canon to the best of my ability with my primary agent, and any secondary agent that I may recruit or adopt at a later point:

Agent S.A.M.S
Species: Self-aware Mary-Sue
Age: Jailbait
Height: 5’8” Weight: N/A
Hair: variable, most often dark brown and 40s military cut
Eyes: Hazel
Department: Department of Floaters
Division: none
Previous Partner: none
Partner: none
Weapon(s) of Choice: Ballast Stone, ice pick, cast iron skillet, and a 30 lb brass bell
Response Center: 1943
Fandom(s): LotR, Hogan’s Heroes, Hetalia, Warcraft, Star Trek, and Avatar
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And a sample of my writing. This was written for a writing contest at school, but for some reason, it was never reviewed by my English teacher for admittance to the contest
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Excerpt from the memoirs of a Space Marine circa 2017--

Love.
It is one word, four letters, one syllable. It has so many meanings. It can be platonic, it can be passionate, or it can be lustful. Love can move mountains and start wars.
Love is defined as a profoundly tender, passionate affection for another person. Love is an emotion, one of the most powerful ones that we, as humans, can experience. So often though, we lock it away, never to be seen or used.
A lot of the time, it is easier not to love. Love can cause you immeasurable pain. Hatred, rage and anger, though? Those are safe emotions.
Those three emotions can be controlled, focused and directed safely.
But love? Love is unpredictable. Love is a wild horse- it can hurt you more than any physical wound ever could. I’ve seen so many broken hearts after the air raid sirens die, or a patrol returns to base. So many of us never come back these days, and we leave our friends and our lovers behind.
Some days, I feel inordinately guilty. I have my lover, a doctor, who stays safe at the base.
I have a lover who isn’t likely to die anytime soon. I love him for it, and at the same time resent him for his safety. He has a permanent post at the base, behind the walls, and I’m almost always on the front lines, buried up to my neck in blood, water, and mud.
Who do you love? Do you hold them close at night, praying that you go first?
Do you love them as much as I love my doctor?
He is a medic, all of twenty one years old. I am a soldier, who has no business being in a relationship with him. Back on Earth, if she had never fallen prey to outside forces and our government’s shortsightedness, we might never have met. Back on Earth, my handsome lover would have a line of men and women falling at his feet, and I would have been miles away in another country. It’s funny what an interstellar war will do to you.
Yet, despite all of this, he chooses to spend his time with me, whenever I can be at the base.
I love him with all of my heart, but does he love me back? Or is our tryst merely a game or a joke to him?
Is it a game to him? Is he in love with me, or am I to be cast aside when someone new catches his fancy?
I am seventeen. My barracks chief says that he will kill my lover the next time that he sneaks into the barracks to spend the night. I worry that someday the Chief will carry through with his threat.
How much do you care for your lover, or spouse? Would you storm the gates of hell itself for them? I would. Would you die for your lover? I love him so much that it sometimes becomes so painful. I would breach the gates of hell to bring him home, and I would die for him. Of that, there is no doubt in my mind on the matter.
Does he love me as I love him?
Love: a feeling of intense desire and attraction toward a person with whom one is disposed to make a pair; the emotion of sex and romance. I read that definition once. It is that emotion, and others, that I direct towards my older lover.
Would you stay in a relationship, knowing that at any moment, you could die? Will you die next to your lover, watching their life bleed out of their eyes, even as yours leaves you?
I would. I would stay in the relationship, come hell or high water. I would die beside my lover. I would follow my heart, even as I pour my soul into these pages, knowing that he might one day see them- perhaps the day that I die protecting the last sorry dregs of humanity from the aliens.
We humans are slaves to our emotions, that much is true. It doesn’t matter if you are black, white, yellow, or bright green with black spots; we are all controlled by them. They dictate our lives according to their whims, even as we try to fight them.
I will forever be a slave to my passions. I will be a willing slave to them, even as I fight them.
Even as I sit here in the mud, rain pouring down my back, writing these words down, I stop myself from eating my gun. I love my partner too much to commit that kind of treason, to myself and my people.
Someday, I will confess my soul to him, but until that day, I’ll sit here in the mud, writing in this journal.
Perhaps someday, I won’t have to shoulder my gun anymore, or pull on a mask that turns me into a faceless protector of humanity, and settle down.
Love: A deep, tender, ineffable feeling of affection and solicitude toward a person, such as that arising from kinship, recognition of attractive qualities, or a sense of underlying oneness.
This is all that I fell when I think of Andy, this and more. I keep his picture folded into my breast pocket, and look at it to remind me why I stay on the front lines.
How much do you care for your lover? Will you die protecting them, will you face down the devil’s spawn that I fight ever day to protect them?
I care for him so much. I will die protecting him; I will face down a horde of the devil’s spawn and more to keep him safe.
No one can tell me that I take foolish risks. I am ruled by my emotions, and I cannot lock them away, merely bury them as best I can. I cannot force myself to become a creature of cold unloving stone. Many others have hardened their hearts to the world; others have merely walked out of the base, and never returned.
There is so much heartbreak here on this planet. It’s an unruly pisshole, but at least we can call it ours. The heartbreak can become unbearable at times. I believe that maybe if we had had forewarning, we could have saved our homeland. But we didn’t and now we are dying by the dozens.
We create, we survive, we adapt. We do these things, and we survive to keep on living as human beings. We aren’t animals, although some of the men and women that I fight alongside make me wonder, and we become.
I am in love, and I know that it is love, not lust.
***
That piece was a little existentialist, and probably more than a little bizzare — but it is one of my better pieces of short original fiction. Also archived on fictionpress.com at http://www.fictionpress.com/s/2649246/1/Love

For my Permission, I linked to a short fanfic I'd written for Stardust, but not all PPCers have written fanfic, so they use what they have - original fics, whatever. I suggest that, if you've written a story of your own (fanfic or original), you should probably use that before writing something specifically for Permission-getting.

Then again, it's also a question of what you consider to be the best example of your abilities. In short, we're not picky. As long as it's not a script or the like - I think that would be a bad idea, since there's no narrative, no flow, no pacing.

my writing sample was the story of my two Agents' recruitment and meeting. Although I did have a fair amount of time to play with, as they joined right before the Macrovirus Invasion of 2008, and therefore spent a month in their RC with no missions and forced interactions.

But a writing sample can usually be anything. Some people have used fics, Agent introductions, or entirely original pieces. It's just so the Permission Givers can get a feel for your usual style of writing.

Hope this helps. :)

I'm not sure, but I think it's generally an example of your fanfiction, or just any story you do, really.