Something that bothers me about the "Author's Guild"
First and foremost, the Author's Guild is a for-profit company. It's not a true "guild" in the legal sense of the word. Unlike the WGA, you're not obligated to join it when you sell a novel.
Second, on their website, they list their dues as: "first year dues are $90. (After the first year, dues are charged on a sliding scale, depending on your writing income, but most members continue to pay $90.)"
I have sent no less than three emails to their contact address asking what the "sliding scale" is. Nobody has ever bothered to email me a response. Nowhere on their website do they list this mysterious "sliding scale." I'm not reassured by their line about "most members continue to pay $90).
There are a lot of for-profit companies out there "working tirelessly to help authors," etc. etc., while taking your $$$. They're just one of many, they don't have the ability to call a strike (unlike the WGA), so to call themselves a "guild" is disingenuous, in my opinion.
If your writing is good enough, find yourself an agent. He or she will be a thousand times better at protecting your rights and giving you advice (sorry, but paying $90 for some pamphlet on contract negotiations that comes in the mail is simply not worth it. Even if you don't have an agent, you can check out books from your local library for free which cover the same topics).