8. Do you write OCs? And if so, what do you do to make certain they're not Mary Sues, and if not, explain your thoughts on OCs.
This question made me realize that I don't think of OCs as OCs. They're just characters; whether or not they originated in my crazy little brain or came from the source material never occurred to me before. Though, I suppose, it should have, as I devote a lot of time trying to depict source characters as faithfully as possible. I find that part of writing to be the most fun, mimicking the characters that I see in the show, so you'd think that I would definitely notice when I've inserted an OC.
The short answer is yes, I write OCs. The biggest one so far is David, the main character of The Actor, who I adamantly insist is not meant to be accurate to the real person in any way whatsoever - he's a complete fabrication. I have another major OC who is the main character of the long story that's 90% done and I keep neglecting - her name is Traci. In addition, in A Teacher and a Housemaid, my ongoing series about the Farringham School for Boys, I've created a number of minor OCs.
I think my main tactic for preventing Mary Sues is to write down the major traits of the OC's personality and stick to them, making sure they're speaking in their voice, not mine. I remember a short list of traits for David: generous, slightly sarcastic, no stage fright but panics in real danger. His character, though, was secondary to the plot, so once I had the plot the mapped out, he just flowed from my proverbial pen to fit what he was supposed to do.
Traci was a bit more difficult. She could easily have been a copy of my personality; it didn't help that I needed to map out her life and chose to have her be born in my birth year so that it would be easy for me to go, "What was happening when she was twenty-five? Oh, this world event happened when I was twenty-five, so that's the right time for her." However, she had different goals in life than I do, and her personality matched them. I did have to consciously give her a bit of in-your-face backbone, to have her stand out just a little bit more.
The minor OCs in Farringham, I pattern after other characters I've seen. For example, the maths teacher, George Andrews, in my mind, looks and sounds exactly like the teacher in "School Reunion" who tells the Doctor that a student told him the height of the walls of Troy in cubits. I keep a list of the characters I've invented for Farringham and what they've done, and note down any salient traits or events.