My other personal favourite in that summary list was "A normal girl (not really) turns out to be a you-know-thing (no, you don't know) & helps the marauders get the you-know-what (well, you don't that either) from you-know-where (or that)."
I believe, that in order to be a very good writer, you have to read some very bad writing as well. This is so you can get a good sense of what the other side is like, and do your very best to shy away from that. Of course, ultimately, you have to write in a style that is natural to you. This takes experimentation.
Word. The final frontier. To boldly write what no person has written before. Which, you know, includes split infinitives and sentence fragments...