Usually, I get the greatest ideas in the middle of something. Sometimes I'm reading a book. Sometimes I'm washing the dishes. Most of the time, I'm at school. 

Ideas just "explode" and I quickly write it down. Then, if I have time, I start a mini plot line of the story-> or at least that event. I have a terrible memory, so I need to write everything down before I forget my idea. 

Once the plot is done, I set aside the idea. Because I have lots of ideas, and I can't write 5 books at once. But sooner or later, I'll get to the idea again, and fill in the gaps. 

I usually write right after reading (a good book- nothing school assigned) because my imagination is overflowing at that point. From there, I usually don't even know what I'm writing until I finish. I know what I'm supposed to be writing, but it doesn't always turn out.