I've decided to write some Fanfiction, the problem is: I don't know who i want to write about more! I'd love some suggestions about who and what, thanks, i'll be posting the stories in this thread.
First of all, start typing word. Get an idea, anything that come to mind. From there, it's much simpler to write a story.
Every pony has their own way of writing, so I can't really tell you what to write, or what to write about - unless I knew you very well (which I don't), you'd probably get bored with my suggestion very quickly. Instead, take a look at other fan fic, and find out what kind of stories interest you. Then write that. But it has to be something that interests you, or the story will die on the vine, so to speak.
Basically, start off with a sentence. Did you notice the sentences in the beginning in most books? Half of the men who wrote their book started with that sentence. Basically, a twist, or a really important fact about the story. Then they base a whole story on that. Though I prefer to write something like a mini-non-dialogue-script, of let's say 5-10 sentences. Then turn it into a full story. If you want suggestions about what to write, I'd suggest you base it on the theme of "hunger and beggars". That would be an interesting experiment.
I have no idea what your style of writing is, but if it's anything like mine, go ask on the chat for a topic, and start writing. It doesn't matter what you write, just write. Then, next day, read what you wrote. Change whatever you don't like, add something maybe. Then, on the next day, repeat. Do this untill you get a story of desired complexity.