There are two things that I find that typically get in the way of the story for me. One is the ever-dreaded, ever-feared Mary-Sue. I have found over the years I have written is that most people do not actually know the definition of a Mary-Sue is. I was one of these people in fact for many years. In case anyone is wondering the easiest definition in a character who is the the youngest/oldest/best/worst/first/last anything. They also can typically do any and everything, or they can do anything right at all and yet everyone loves them. I have written many many Mary-Sues in my years of writing. There is an excellent site that is the "Ultimate Mary-Sue Quiz" if anyone is interested.

Note: The other thing that bothers me is not necessarily SFW and so will be posted on my personal journal and I will link in comment.