I've blogged a lot about things writers can do to promote their books.
Here are some things they shouldn't do, both on the self-promotion front and in service of their careers.
Don't be pushy. Ever. It's about what you have to offer, not what you have to sell. Your main goal in self-promotion should be finding and meeting people who are looking for your type of book.
Don't be self-absorbed. If all you talk about is you, people will tune you out. A conversation isn't a monologue. Give and take should be part of all human interaction. No one wants to listen to you toot your own horn.
Don't be boring. Unfortunately, boring people never think they're boring. Short of videotaping yourself to see how you act, try taking your cues from the people you interact with. Do they seem into you, or anxious to escape? The better you can read your audience, the better you'll do.
Don't feel entitled. Yeah, you work hard. Good for you. That doesn't mean you deserve to be published, or you somehow earned your success. You got lucky. Feeling like the world owes you, or acting like God's Gift, is a sure way to annoy potential fans.
Don't be ungrateful. Being thankful, gracious, and helpful goes a long way. Don't bite the hand that feeds. Your fans, and anyone who helps you on your journey, deserve your attention and praise. Give freely of your time.
Don't be bitter. Yes, you got screwed. We all get screwed sometimes. Complain to your mom and a few close friends, but let the public always see you as successful.
Don't be defensive. There will be critics. There will be suggestions. There will even be people pissed at you. Don't take any of it personally, and diffuse the situation by listening to them and thanking them for their time. Once you put up your dukes, its hard to put them down again.
Don't be needy. Sure, you want to be read. Yes, you want your time in the spotlight. But fishing for compliments and begging for scraps are pathetic and embarrassing. Act confident at all times.
Don't be unprepared. You're a professional. There's no excuse for not giving 100% in everything you do that's related to your profession.
Did I miss anything?