I have lots(!) but I'm particularly thinking of my tendency to forget to describe the setting of a scene (@Pamela Jo reminded me of this - thank you!). I picture it in my mind as I type but I'm too focused on the characters' actions and dialogue to record what it's like where they are. I don't mean lots of purple prose, just something. I have to go back and add bits in. I heard an interview with Gilliam McAllister and she writes several drafts so that she can focus on one aspect of narrative at a time and then adds layers with each subsequent re-write, which is an interesting way to think about what it takes to create a polished novel.
What's your Achilles heel?
What's your Achilles heel?