The Favorite Story option does not mean I favorited a story. It is the only available method to bookmark a story and get update notifications. I download stories, and read them on a mobile device. Hence, knowing that updates occurred is important.
It means I am reading or plan to read a story. It might also mean that I actually favorite-ed it.
There is no reason to comment on a favorite. Really.
Laws of Fanfiction
By Eliezer Yudkowsky / Less Wrong
The (first) Three Laws of Fanfiction
Rule One If you do anything to increase the protagonist's power, or make their life easier, you must also amplify their opponent or add extra difficulties to their life. You can't make Frodo a Jedi unless you give Sauron the Death Star. Otherwise, even if it is well-written in all other ways, your story will suck because the reader will know to expect an unending string of easy victories, leading them to neither wonder or care about what happens next. The Mary Sue is not defined by her power being too strong, but by her challenges being too easily overcome.
Rule Two Originality isn't easy, but it is simple Just don't do stuff that's already been done. Even if all of your other characters are going to be absolutely true to canon, you still shouldn't have Harry Potter facing the same three challenges in the Triwizard Tournament because we've already read about them a thousand times. Put in three different challenges. Seriously. It can't hurt. Don't just go through the same events everyone has read about a thousand times before. Writing fanfiction lets you borrow the characters and the world; it doesn't exempt you from needing to surprise the readers and give them something new to read.
Rule Three The premise of a story is a conflict and its resolution - someone with a goal, which they take action to achieve, and severe obstacles that they must replan to deal with (not just speedbumps along the way), and some ultimate resolution of the conflict in which the people and their situation have changed. What happens if the Terminator is sent back in time to kill Voldemort is not a story premise, just a fleeting mental image. What happens if Harry Potter is under constant attack by shape-changing robot assassins is still not enough of a premise. Harry Potter is under constant attack by shape-changing assassins, and by the time he manages a spell to wall off the future he's already learned not to trust anyone could maybe be a story's premise (though you wouldn't put that in the summary, or tell any reader that until the story had ended). You can change this plan later - but you should at least have one to start with.
So if you have a lovely mental image of Frodo with a lightsaber
1. Figure out how to make his life more difficult, to make up for the lightsaber.
2. Decide what's going to happen differently in your fanfiction than in the other ones you've read.
3. Know what Frodo wants and what's going to get in his way, and have a plan for how it will all end.