Certain backgrounds, and making last minute corrections are consistently the most tedious parts for me. There have been many pages where I didn't catch inconsistencies between panels until the last step of the process. It's so annoying because I was just about to finish the page and add it to my buffer, but I'd rather correct those errors at the last minute than to not notice them for days after uploading the page!
I use vector graphics, which makes architecture easier for me to draw, and keep consistent compared to when I draw them freehand, but nature backgrounds are much more difficult and tedious to draw with vectors.
Thumbnailing page layouts is sometimes easy for me, but only if I have a very clear idea in my head for how I want a page to turn out. At other times I don't have such a clear idea, and then it's tedious using trial and error to figure out the angles, what type of shot I want to use for each panel, and how many panels to put on the page.