What you need to know:

Harry/Ginny
Teddy/Victoire (Harry Potter)
Rory/Logan (Gilmore Girls)
Meg/Calvin (Madeleine L'Engle)
Marching Band (no flutes though)
Ben/Sadie (Naturally Sadie)
Derek/Casey (Life with Derek)
Isabella/Phineas (Phineas & Ferb)
Mia/Nicholas (Princess Diaries movies)
Zoe/Zane (Eureka)

Pet peeves on fanfics include poor grammar, poor sentence structure, word choice, sentence fluency, ACCURACY, ACCURACY, ACCURACY. If you're writing fanfiction about a story, you better damn well know all there is to know about it. If you blame spell check or auto correct I will not forgive you. Getting off on tangents is obnoxious. I will not read stories with less than an average of 1000 words per chapter. DO NOT WRITE OUT CONTRACTIONS!! It makes me think that you're still in grade two and haven't yet grasped the concept that the way we talk and the way we're taught to write are two entirely different things, and it's a different monster entirely to write out two people speaking.

Not fond of BritLit.