Plotting is my biggest weakness, and it's the reason I only write short stories. I tend to keep plots simple and small-scale, as anything else tends to be a struggle for me. I also find that creating a satisfying ending can be tough, but I've gotten better at finding ways to tie everything together at the end.
I don't really have a problem with characters for the most part, however in my latest fic I did struggle trying to get the voice of Aarune, the secret base expert, right. I had written the whole fic already when I realized I had to go back and try to make Aarune's dialogue sound a bit less generic, but pinning down his voice was a bit tricky, just because he has such a distinct, colourful way of speaking in ORAS. I read his dialogue on Bulbapedia and think I did a decent job in the end, though!
~Psychic