I would say that the contest should be for poetry (all forms: traditional and free verse) and for prose (especially short stories). Interesting would be to include also visual and found poetry.
There should be a word limit between 1,000 and 2,000 words as stories are a bit longer and there also exists ballad poems that can be quite long, too.
Well, I have read that the fav theme is fire/passion.
I would it define a bit more open and suggest "light". "Light" can be fire, too or a bonfire as well. A heart full of "light" can be a heart full of "passion". Most important is that you are not bound to a specific topic as light means not only fire, it can also be hope and many other positive things. The theme should be one that is positive and uplifting, gripping (not in the sense of horror, but in the sense of moving a heart/a person).