Disclaimer: I have no inside information on how the staff and instructors judge and evaluate the submissions. There’s no magic formula or shortcut for admission. Instead I’ll tell you what I did to get in, and hopefully that helps a bit.
I heard you have better chances when you turn in your sample well in advance before the deadline, to give more time for your piece to be thought over. Take this with a grain of salt, though. I submitted in February, months before the June deadline. I mainly did that so I could pay only $25 for the fee, rather than $50 that comes with skirting the deadline.
Submit something you’re close to and proud of.
Of course every work you create is precious, though some you hold close to more than others. It’s natural for writers to impart their experience into their works to some degree, more or less. For VP I submitted a 4k-word slipstream short: my weirdest, most experimental and personal one yet. And I don’t really read or write weird fiction. Apparently there’s a sort of stigma with first-person present-tense…oh well I did it for this story, anyway. I played around with the story’s theme and structure, how far I could stretch myself with language and sexual content, which I read and use sparingly. I relied on a strange combination of allusions to the 70s song “American Pie” and Dante’s epic poem Inferno as structural and thematic framework for my story. It felt somewhat like a dare, and I felt somewhat vulnerable in sending that story, though I’m glad I took that bold step.
Don’t try catering to the instructors’ tastes in hopes to get a leg up. Look instead into yourself, and send a story that best reflects your interests and writing abilities, if possible. I’m told that the cover letter doesn’t matter so much as the writing sample. Use that opportunity to put yourself in the story, in however way you want, through the protagonist’s voice, character(s), setting or situation.
You are free to submit a novel excerpt; in that case it’ll work a lot like the novel query process. Personally I thought it would be better for me to show how I can start and end a story in its entirety.
Submit something you’re willing to set aside and do nothing with until rejection, or October (if you’re accepted):
Once it’s off your hands, don’t touch it! Work on something else to take your mind off the submitted piece. Take it from me: I confess that I’ve made a few revisions to my story following the submission, and after acceptance I was told by one of the staff that I’m not allowed to present a newer version of my submission for critique, since the instructors have already looked over and commented on the version I had sent.
Don’t give up!
It’s very common for people to get in after many tries. Persistence is the true judge of a writer’s character. If you really want something that badly, get up, dust yourself off, and jump back into the game. I know it’s really hard, but try not to take a rejection personally. There are way more applications than spots in a workshop, especially for big ones like Clarion, Odyssey and Viable Paradise; that makes for lots of hard decisions and close calls on the staff’s end. If money and time for workshops don’t end up working out, don’t feel like you’re less of a writer because you didn’t get into or graduate from one. I know plenty of absolutely amazing writers who never attended a single workshop.
In the end, there are lots of factors beyond an applicant’s control, but I hope these pointers help you put together your application and think over some things.