Yep, posters are good! Seen a lot of brilliant ones out there.

Like the poster Greasybacon made for my story, isn't it nice?

But if you know that you honestly can't edit good, don't. 

I can't count the amount of times there have been stories with great plots but sadly the readers have seen a bad poster and thought 'er- no.'

If you want a good poster, there are loads of graphic designers out there willing to spend some time making one for you.

If you are an account for graphic designing/poster and background making for stories send me a message and I'll make a list here to promote you.

But remember, authors, a story can still be amazing without a poster, you don't need one. The story is all in the words you write after all. Not something you see.

Unless they start making movies of fanfictions one day. *please please please*