I am no writer by any means, but I did write a few unfinished fanfics.
There is always one character in a series that stands out more than the rest to me, usually a character I really start to admire, even adore. I take that character and put myself into a story with them.(I say myself, but of course I am just a stand-in until I developed 'my' character more and name her)
It always helps to have a good imagination, and I always had an over-active one
I concocted a story in my head about traveling with the main character, what kinds of things would we would encounter along the way... dangers and even some romance(I am a sucker for romance*wink*) I just sat down and started writing all my thoughts on this, traveling with my character(that I secretly adored) even if it was just typing notes. Thinking back on it. the story wrote itself.
What was odd for me is, I started writing the middle of the story 1st, then I went on to write the beginning. (?.?) lol but I heard that is pretty common.
I really had to unlock a door to my mind, because when I first started, it was very straight forward writing. I would slave away over the pc, finish a section of story, wipe the sweat my fore head, and take it to a friend to read, only to have them read it, then look up at me and say "Yeah, that's a pretty good draft." ( >.....................< ) Whaaaaaaa? DRAFT? In my eyes it was gold! but upon re-reading it, and looking at it through their eyes, I would realize... crap (-_-) it is just a draft, it lacked detail!!!! and the detail is what was so hard for me, the endless descriptions. This is what I was talking about with the 'unlocking a door to my mind.' My story lacked a certain scope, I needed to take a look around me and describe what did the terrain looked like, what kind of noises did we hear, for Gods sake I had not even described my characters attire, or what we looked like. Guess we were just running around the woods naked then. lol

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ok, I am rambling...
Sorry I am not much help, but these are some challenges I dealt with, yours may be different.
Just write out ur ideas, even if it's a loose draft or notes, and then make them grow..... I actually kinda envy you, I have not worked on my fafic in a long long time. I enjoyed writing it more than people enjoyed reading it, lol good luck
