>>149665341
Paneling, actually. I can draw the images separately easy enough but figuring out an interesting way to organize the panels, that leaves as much space for the characters, dialogue and backgrounds while also leading the reader's eyes around the page is really difficult for me. Not enough people talk about how important good paneling is on a comic. It can basically make or break readability.
Backgrounds are a pretty big weakness of mine too but this is a specific issue I have with making comics in general.