Advice for Authors

Lower your expectations. The happiest authors are the ones that don't expect much.
The best time to start promoting your book is three years before it comes out. Three years to build a reputation, build a permission asset, build a blog, build a following, build credibility and build the connections you'll need later.
Pay for an eidtor editor. Not just to fix the typos, but to actually make your ramblings into something that people will choose to read. I found someone I like working with at the EFA. One of the things traditional publishers used to do is provide really insightful, even brilliant editors (people like Fred Hills and Megan Casey), but alas, that doesn't happen very often. And hiring your own editor means you'll value the process more.
Understand that a non-fiction book is a souvenir, just a vessel for the ideas themselves. You don't want the ideas to get stuck in the book... you want them to spread. Which means that you shouldn't hoard the idea! The more you give away, the better you will do.
Don't try to sell your book to everyone. First, consider this: " 58% of the US adult population never reads another book after high school." Then, consider the fact that among people even willing to buy a book, yours is just a tiny little needle in a very big haystack. Far better to obsess about a little subset of the market--that subset that you have permission to talk with, that subset where you have credibility, and most important, that subset where people just can't live without your book.
Resist with all your might the temptation to hire a publicist to get you on Oprah. First, you won't get on Oprah (if you do, drop me a note and I'll mention you as the exception). Second, it's expensive. You're way better off spending the time and money to do #5 instead, going after the little micromarkets. There are some very talented publicists out there (thanks, Allison), but in general, see #1.
Think really hard before you spend a year trying to please one person in New York to get your book published by a 'real' publisher. You give up a lot of time. You give up a lot of the upside. You give up control over what your book reads like and feels like and how it's promoted. Of course, a contract from Knopf and a seat on Jon Stewart's couch are great things, but so is being the Queen of England. That doesn't mean it's going to happen to you. Far more likely is that you discover how to efficiently publish (either electronically or using POD or a small run press) a brilliant book that spreads like wildfire among a select group of people.