Thanks for the mentions, Steph and Steph!
As far as what I find most difficult... I used to struggle the most with description and character development, but I've gotten a lot better at those. For someone who doesn't talk a lot in real life, dialogue has always come easily to me - I guess when I'm not talking, I'm listening, so that helps!
I think what I struggle most with nowadays is just staying focused and inspired enough to write and write well. Between collaborations and my own stuff, I've accumulated too many projects, and it's hard to stay inspired on all of them and find the balance needed to write them all. I know what it's like to be so inspired that the story almost writes itself, and so when I'm stuck with a story that just doesn't go that way for me, I get frustrated. If the writing's not flowing as well as I want it to, I tend to give up and try to work on something else, and so I end up jumping around from story to story and not finishing anything. I didn't used to be one of THOSE writers, so it's annoying that now I am! It just takes me forever to finish a story anymore, and it's hard to stay committed to one project for years at a time before allowing myself to move on to the next one.