Ten Ways to Rewrite a Show

Henry Jenkins in "Textual Poachers" includes a section about ten different ways a show can be rewritten as a fanfic.

1. Recontextualization - Filling in the gaps in broadcast material and providing additional explainations for characters' conduct. See Fan Wank and Fix Fic.

2. Expanding the series timeline - Either into the past or future. See Continuation, Prequel and Backstory.

3. Refocalization - Shifting attention away from the program's central figures and onto secondary characters (often women and minorities). See Day in The Limelight and Lower Deck Episode.

4. Moral Realignment - Inverting or questioning the series' moral order. See Deconstruction/Deconstruction Fic, Alternate Character Interpretation, Perspective Flip, Die for Our Ship and Draco in Leather Pants.

5. Genre Shifting - Telling stories different in tone and style from those of the actual series. See Characterization Tags, Dark Fic and WAFF.

6. Crossovers - See Crossover and Fusion Fic.

7. Character Dislocation - Characters are removed from their original situations, and may be given alternative names and identities. See Alternate Universe Fic and Transplanted Character Fic.

8. Personalization - "Mary Sue" stories, and stories that break the fourth wall by having characters interact with fans. See Mary Sue, Marty Stu and Self-Insert Fic.

9. Emotional Intensification - Including the "Hurt-Comfort" genre. See Hurt Comfort Fic.

10. Eroticization - See Lemon, Lime and Porn Without Plot.

of course, these are the rules of fanfic. If you're a pro, just stick 'em on a rocket. If you are interested in more ideas about writing fanfiction see So You Want To Write A Fanfic.