One of the main ideas that has come to mind numerous times is a feature that would allow you to group your stories together if they're in a series and allow ratings of a series and not just the individual story. Something like;
"If you enjoyed this story you can find the full (INSERT SERIES NAME HERE) series of stories by clicking here."
So instead of just linking one story at the bottom of a submission a link to a group that lists all the stories can be put there. It would make finding all the stories in a series much easier, especially if they don't have consistent names like "Chapter 1" etc and its hard to tell without clicking into the story if it relates or not.
Rating the series would be a great feature also so that people can tell if its a worth reading them all etc. Maybe keep ratings for the individual stories and then give the average rating of all the parts combined on the group of stories page?
Anyway, that's just something that came to mind and I hope to see implemented at some point!
Active Ink Slinger