Welcome to the community!
My top weakness as an artist are those FREAKIN' BACKGROUNDS!!!!! I usually draw pretty fast, but with backgrounds, it takes me forever. I just suck with perspective. Which results in not overly complicated backgrounds. Oh! I also suck at hands.
As a writer, I'd say it would be the fact that I write WAY TOO MUCH!!!! My chapters need to be severely edited each time, because they all end up too long and I can't have a 50 page comic book, because I print. My spelling could use some work too, but overall, my person who does my proofing doesn't have that many corrections on my latest chapters.