On the topic of ideas, I would actually try to incorporate the new ones I thought in my current fanfic (whatever that may be), and it worked well. If they're not ones I can be able to fit to the current story, either I turn it into a one shot or save it for another story.
What gets me frustrated is there's one fic you want to write but can't get new ideas for it pop up yet. When you do have ideas, it would fit better as a totally new story. @_@
What is your greatest enemy in writing (ignoring writers block)?
Like Feign, the time issue and I can attest to that. I've been given a lot more responsibility in real life now than ever before, so I have to take care of that first. Even though this summer I can be able to have time to write another chaptered fanfic, I didn't because actually all of a sudden got a lot of things to do. Hence, why I wasn't able to finish my two one shots yet...long ones. ._.
Another thing is grammar. Whenever I proofread, I get worried if I have awkward sentences or used the wrong tense. I know I won't be able to catch them all, but I'm paranoid that I have a load of those mistakes in my chapter. x_x