Okay. How about this, it was a roleplay I've created once before so we'll use that for our prompt. *runs to get the discription* oh bugger, not there gotta write it again.
Each era has been murged together by Harry Ron and Hermione, they were hoping to get back to the years of Tom Riddle but miserably failed (oh poor trio) and now instead each era goes to school together, most are in their 7th year (potter ect) but some like ginny are in the year they would be in the 7th book. Ta DA. PROMPT (it wasn't this sucky before)
None, write the way you want, read how other people write and adapt their style. All I ask, have fun, If I feel the need to start placing rules, I will.
So post in responses here we'll see how that works. I think it'd work best to put who you are where you are and who you're talking to in the comment title.