What have you learned from design that helps and improves your writing, and vice versa?
This is going to sound odd, but almost nothing in one can "improve" how well you do in the other. Design has helped me appreciate how hard it is to typeset text, to lay out a magazine, to make a book from start to finish. But I think learning an appreciation is about where it ends. I know that good typesetting can make poor writing look good but still read poorly. Thinking about how my writing is going to look on the page can often hijack the writing process, distracting me into thinking about the design of the whole book before I've written a single chapter. But in certain projects, I have been able to combine the disciplines into a single effort, envisioning the design and writing as part of, more or less, one idea. The Dead Bug Funeral Kit is a good example. I had the idea. Then I looked over all the ways I could construct the kit, meaning I thought first about the design of it. Then when I had the kit done, I worked backwards from the end result to fit the writing into it. I wrote the poems a certain length to fit the page. I wrote instructions that could fit on a scroll. I designed labels that would look good with the limited means at my disposal. That's a good example of design and writing combining within a single project and reinforcing each other so that the whole is greater than the parts. Magazine design is another area where I might be able to say that design and writing reinforce each other and lead to better results, but only when I'm able to both write and design and conceive of them together. In most other areas, I improve my writing only by reimagining and rewriting, not by designing and redesigning.
The vice versa (whether writing has improved my design) probably deserves the same answer. I have a respect for words when thinking about design, I know how you can so easily affect the interpretation simply by adjusting the design of the words, and I might use text differently within a design because I'm a writer. For example, I wrote a short story to fit on a bookmark. This is something a writer is more likely to do. But whether being a writer improves my design is a separate question. I think my love for writing influences my designs, but I also think I'm as likely to screw up a design because I'm a writer than I am to design better.