I love to read stories on fanfiction.net too, but I don't believe it is a good place for new learners. As cherrydonut stated, the quality can vary very greatly. Some I felt should really be published if it was allowed, while others I suspect that the authors had never graduated from elementary school. I had to close my eyes to countless glaring grammatical and spelling errors. The website, while containing quite a few jewels, is littered with junk written by daydreaming fans. One who is unfamiliar with the English language might easily be misled, not to mention that many of the worse stories also contain lots of profanities and swear words. My teachers would be horrified.
P.S. When you read English novels, there are probably quite a few words that you won't understand. I wouldn't recommend looking every one of them up in the dictionary, because that would really spoil one's appetite for reading. Instead, just try to understand the general idea of the story and search for the recurring words.
P.P.S. My favourite fandoms are Harry Potter and Narnia. Especially Narnia. It's such a pity that almost all the stories have Mary Sues and too much romance... *Sigh*
