There are some very helpful screencasts here, but I think a few things have changed due to the original version of the form being so large.
1) Give yourself PLENTY of time to work on it. You'll want to decide on which 3 to 4 requests you have from this fandom list ahead of time.
2) Make a text document with your characters (in the format from the list) and a summary of each of your 3/4 requests. Below that, make a list of the 4+ fandoms and characters you are willing to write. Copying and pasting into the form is much faster than using the autocomplete, and if you get an error after hitting submit (MANY PEOPLE HAVE) then you have a back up.
3) Watch the screencasts to see how to do the "bucket list" offer. This is where you can offer to write a large number of fandoms without specifying characters. Only use it if you're willing to write anything, though!
4) After you're done filling out the form, if you get an error, try refreshing a several times before headdesking yourself into a migraine. Then take a deep breath and come back to it with your text file handy. Some people are finding that it's easier to do a bare bones signup, and come back later to edit.
5) When you're finished, there is a list of links to the left. The story summary link is down right now. Soon, I hope it will be working, and we'll be able to see which fandoms have been requested and offered.
I made 4 requests, 7 specific character offers and 32 bucket list offers. I love the adrenaline rush of not knowing which fandom I'll get.