1. What is the single most important thing an aspiring writer should know?
You need to constantly work at this; getting published isn't as easy as it looks. If you think you should only write "when you're inspired," then please get off the writing train. This is not the business for you. Writing is work.
2. What mistakes do aspiring writers sometimes make?
Overestimating their own brilliance. Seriously. Not listening to guidelines, and not following instructions. At one CWC, an agent told a few writers, "Please send me a query." These writers emailed her *their entire manuscript.* NO! If you don't know what "a query" is, read about it, or ask someone who will know! To ignore instructions means a second chance is not likely.
3. How important is networking for writers?
Crazy important. Not in terms of getting published, but in terms of building your own personal network, your first readers, your supporters. One thing I have to say about Chicago -- our lit community is really supportive. So get in there and be a part of it!
4. Are there any practical guides to writing and publishing that you recommend?
Writer's Digest and Poets & Writers (magazines + online) have good, up-to-date articles and advice. I also like to consult the Writers Market online version (vs. the annual book) - it's always current because names and positions change so much in this industry.