First, I want to start with the general definition of fanfiction.

*ahem*

Fanfiction
- A fictional piece of writing created by the fan of a singing group, anime, movie, TV show, or anything else of that nature.
A fanfiction does not have to be true to life, and usually contains fictional events.
A fanfiction is the creation from one's mind translated onto paper. (or in this case AFF)

That's my definition of fanfiction.
Don't like it?
haters gunna hate

Anyway,

to some, starting a fanfic is one of the hardest steps of writing.
Here are some tips to get ideas flowing.

oo1: Decide on these three items.
- What will be the main plot?
- Who will be the main characters?
- How long will my story be?

If you have a great idea for a plot in your head, go get a piece of paper and write it down while you can. Inspiration can hit anytime, such as in the shower, so be prepared.
With the idea of plots being said, do your best to stay away from over-used plots. If you use a slightly cliche plot in your story, but you put your own twist on it, that is what could change your story from good to great.

Writing a story about characters you like will make the story more enjoyable for you to write. If you don't like a specific pairing or person, then don't write about them.
Sometimes you figure out the plot before the characters, or the characters before the plot.

If you have a general idea of your plot, then you can estimate the general length of your story. Whether it be a oneshot/twoshot, a short chaptered fic, medium length fic, or super long, that way you can judge on the flow and speed of your story.

oo2: Write from your heart.
- Yeah this seems cliche, but a fanfic shouldn't be written only half-way. If you have something on your mind, write about it.
With fluff, you should put all your effort into making it seem as fluffy and cute as possible.
Same with angst and romance, put all your effort into portraying the emotions of the characters.

oo3: Real life situations.
- Sometimes you could be walking with friends or what-not, and see this funny looking tree that sparks an idea.
There are fanfics based on real life situations, so don't be afraid to put part of your own life in your fanfic to make it seem more true to life.
 

{I will be updating this as I remember more things}