So, today I learned that if you're new to Yuletide, the tutorial video is fourteen minutes long, and filled with incredibly unhelpful jargon, to the point that they could do with a glossary. Here's a (hopefully) brief introduction to the signup process, and then there'll be another post about Yuletide itself, and finally my 'Dear Yuletide' letter.
Step One - Nominations and selecting fandoms.
The signup sheet asks you to nominate four fandoms that you'd like to receive fic for. This year (2011) is notable in that everybody got to nominate only three fandoms for selection at the very beginning, thus making the list of available choices a fair bit smaller than it was last year, and hopefully stopping the website from falling over when everyone tries to use it at once.
If you start typing the name of a fandom in the signup form (available here, but you'll need to be signed into AO3*), it should autocomplete the names of fandoms, but that doesn't really help you see what's going on. An easier way is to visit this post, which has separated all the fandoms by category and sorted them alphabetically. The 'uncategorized' tab on that webpage has everything that doesn't already exist on AO3, so be sure to check everything. It's a long process, but worth it. Make a list of fandoms you'd like to receive for (you're allowed to select four) and ones you'd be comfortable writing (you must select at least four).
*Archive of Our Own.
Step Two - Prompts.
Open up a word document. Write the names of the fandoms you'd like to receive. Looking at the list of fandoms in the link above, note the characters that have been nominated. You can either request particular characters from this list, or leave it up to the author to select characters for you. If a character you'd want isn't listed, then unfortunately you can't request those specific characters this year. Make a note of which characters you'd like to receive.
Now, for each fandom, write a prompt. The most helpful prompts are those that give the author a whole bunch of options about where they could go with your story. Less helpful prompts are those that say 'anything' (a blank page and no guidance can freak authors out) or those that have one very detailed plotline that you desperately want (which can do two things; either make your author freak out about filling your every request, or make them say 'if you know what you want so bad, why don't you write it?').
A good analogy is buying tea for a gift. If the recipient just says 'I like tea', then you'll be paralysed in front of the shelf. If they say 'I like Black Peach, and if I don't get it, I'll die for srs', problems might arise if you can't get Black Peach. The best help is 'I don't generally like green tea, but I do like black, and anything peach-flavoured is good. If you can do both, great.'
One other important thing to do is let your author know what you don't want. If you hate a character with a vengeance, say you would prefer it if the fic didn't focus on that person. If non-consensual sex, or sex at all, would make you a sad panda, let them know about your 'personal preference'. Make it clear what you don't want, without being pushy or insulting. I received a request last year from someone that disliked a character, and it was phrased in such a way that if I was a rabid defender of that character, it would have made me resent the person I was writing for. So be nice.
Done? Great. On to...
Step Three - The Sign-up Page!
Start typing the name of your first 'I wanna get' fandom in the first box. It should autocomplete. Write down the characters you'd like to get, or leave the box blank if you don't mind.
If you have a LiveJournal, or some kind of fannish blog, take the word document you wrote in Step Two, and publish it to your blog. Call it your 'Dear Yuletide' letter. Take that URL and paste it in the space where it says 'Website/Journal/Dear Yuletide Author'. If you don't want to give your author a link to your blog, leave that space blank, and put the prompt you've written for your author in the space below that, where it says 'Optional Details are Optional'.
Repeat for your other three 'I wanna get' fandoms.
Step Four - Offering to Write.
Below the requests section, there's the segment for writing offers. Start typing the fandoms you want to request (you must offer at least four, generally up to six, or more if you're mad like that). Below that, type the characters you're comfortable writing. Make sure you're okay with writing the characters you offer. If you get matched up on those characters, you'll have to write them. No options.
If you're seriously okay with writing any characters for that fandom, check the 'Any' box.
Done? Click submit. You're signed up for Yuletide.
What Happens Now?
You'll be assigned to write a story for a reader. You'll be matched up because they requested a fandom you offered to write. Your request will be assigned to another writer.
You'll receive a list of all the requests your reader made. You can choose to write anything they requested, although you'll likely only have the one fandom in common. This is important in case you just cannot write what they've requested. It's uncommon, but it happens.
The only requirements are that you must write in the fandom, and feature the characters they've requested for that fandom. All their optional details are just that - optional, but you should ideally try to tailor your story to them as much as possible. After all, you're giving them a gift. Unless it makes your life unreasonably difficult, try to get them what they want.