At the time I'm sending this to Elsa, I'm still working on my first real epic, and I have one completed shortfic and a handful of SPAMfics under my belt. You've read through Elsa's essay and Mike's new character rules. With a last rush of resolve, you cast your work into the void of cyberspace. Editing is essential. A prereader is a good idea, especially if you slept through high school English.
Penmanship is important.
These are the email equivalent of bad handwriting. The most common of these is poor formatting. If your fic reads like this sentence, and it's not for dramatic purposes, the odds are, many folks will skip it just to avoid the eyestrain. A second category of unreadable fics contains those which are sent as some kind of attachment. Attachments work differently for different email systems, and some folks, myself included, have limits on downloading files.