Edited to Add: A person who wishes to remain anonymous sent me a better version of this post, which I am copying in entirety below this paragraph. Also, I apologize to anyone I confused or annoyed by
drunk-posting to the comm. (I link only so you'll see that it was a special event. You do not need to worry that I have an alcohol problem.) I promise not to do it again.
If any Yuletide newbies are reading this, I hope you're not too confused. In the spirit of clarifying things:
What are Yuletide letters? When you sign-up for Yuletide, you'll be able to choose from between three and four fandoms to request fic for. For each fandom, there will be a space in your sign-up where you can write optional details about what you'd like to see in your fic.
Many people like to write about their fandoms in a more in-depth way than that space allows, so they write a letter to their author, post it in their livejournal, and provide a link to it in the comments of the Dear Yuletide Writer post that goes up every year -- if you don't want to create a livejournal post for your letter, you can also just type it out directly in a comment to the post itself. You can also provide a link to your letter in your sign-up.
Previous years' posts:
2011,
2010,
2009,
2012.
Letters are completely optional and can include many things. People might write about what they enjoy about the fandoms, or what they enjoy to read in fics in general, or they might provide optional prompts, etc. While letters are optional, many authors find them useful, and many authors like to read through them to look for treats that they can write.
If you're unsure of how to write a letter, you can read through other peoples' letters until you figure out what you would like to include in yours. Tips from previous years can also be found here
here and
here.
When you link to your letter in the Dear Yuletide Writer post, here is a suggested format to make things easier for the kind nonnies collecting information about the all the letters in
an easy-to-search spreadsheet. Link to Your Letter
AO3 Name (the name you signed-up to yuletide with)
Fandoms: (written as they appear on AO3)
fandom #1
fandom #2
fandom #3
fandom #4 (optional)
ETA II: If you change or add fandoms between now and when signups close, please add a NEW comment to explain this! If you edit your original comment, that change will NOT be reflected on the spreadsheet.
The spreadsheet Yuletiders are not going back through the comments or tracking the post for changes. They just take new comments and add them in, so: a brand new comment linking to the old with the changes is the best way to make sure the spreadsheet is accurate!
(That, or chase one of us down in #yuletide.)