I don't know how many people here are unfamiliar with the term impro or of how much dub and ogre oriented you guys on this, but here are some helpful tips on writing impro.
First, is from the help page of the site that started it all... er, started the fanfiction aspect, rather. A guide to impro-writing:
http://www.improfanfic.com/imprology.php
While the strip deals with Improfanfic in particular, just ignore most of the things that deal with the site and you'll get a general idea on what impro-writing is about. :)
Next, if you'd like to practice some impro writing right now... as in RIGHT NOW, I recommend going over to our little site Indie Madnesse and browsing the impros over there:
http://indiemadnesse.sandwich.net/
<Insert blatantly obvious encouragement to "Sign up!" here>
Browse the Hall of Fame and Infamy as well to see some samples of how an impro fanfic can turn out/end. This is also to prepare you to keep your cool on what happens when you submit a starter... meaning no whining and flaming about "said author wrote so and so and that shouldn't be!" (unless the impros here are moderated or something?)
And lastly, some discussion on the Indie Madnesse message board that deals with the Rules of Impro (tm) as shared by W4 and the rest of us. I think it's good reading (and better if discussed further) for impro newbies so that future problems might be limited: