With small exchanges, I try to keep an eye on the requests and copy and paste the ones I might be able to write into a separate document. It only works when there are a few sign ups a day though; I wouldn't want to do it for, say, Yuletide.

For Darkest Night, I found it useful to save things off because there were a lot of requests in fandoms I could write that were asking for pairings or freeforms that I really couldn't. I wanted to be sure I wasn't going to match on those because I'd end up writing something that wasn't what the recipient actually wanted. I also wanted to be sure that I was offering the right freeforms for the requests I could write because a small exchange with that sort of complicated matching has to be hard on the mods.