My biggest problem lies in finishing a fic. Every time a plot bunny strikes me, it spins out of control in my head, and I get so excited over it that I have to start writing it. I slap down the first 1-10k words within a matter of minutes, and then as suddenly as it appeared, my great idea vanishes. Just like that. The motivation to write the story dwindles away, and I'm left staring blankly at the ten or twenty pages I just wrote, wondering what the hell I was thinking. It's almost like I've got bipolar disorder when it comes to writing. I'm stuck in a cycle of alternating periods of mania and depression. I know I'm not the only writer out there who has trouble completing all of her projects, but (and forgive me if this sounds self-centred) I feel like my case is one of the more extreme ones. I have over 30 unfinished stories sitting my WiP folder (two of which I started yesterday, in fact), and most of them have good concepts, good beginnings, and sometimes even good endings, but I just can't find the will or inspiration to continue them. For those of you who have read (or are reading) one of my novel-length fics, you've probably noticed that they tend to drag in the middle. That's because I was trudging through mental quicksand towards some distant glimmer of creativity on the horizon at the time :P
I'm trying to fix my problem by working on my outlining skills. I'm one of those people who despises outlines. Whether I'm writing an essay or a fic, I don't have the patience for outlining. I've always considered it to be a waste of time -- why would you spend so much effort putting together an outline when no one's going to see it? TBH, I still don't do any kind of prewriting when I write essays for school unless the professor requires me to. However, I recently started outlining my fics before writing them (mostly thanks to nqdonne, who encouraged me to do so with my hd_worldcup fic), and so far I've found it very helpful. I used to just write down any ideas that randomly struck me during the writing process so that I could use them later, but now I actually sit down before I get too far into a fic and map out the whole story, scene by scene. It helps me control for gaping plot holes (something else I struggle with) and gives me a good idea of whether my out-of-the-blue idea actually has potential. That way, I don't have to waste my time writing the beginning of a fic that isn't going anywhere (or at least too much of the beginning, because I still have trouble containing my impulses to write whatever pops into my head).
So, that's my biggest issue with the writing process. What about you guys? I'm really curious to hear how other writers overcome their weaknesses.