2. Don't badmouth your current or previous employer
Just like in an interview, keep your rants about your boss or company to yourself. If hiring managers see that you're willing to trash a colleague online they assume you'll do it to them, too. Plus, there's always the possibility of getting fired if someone sees your negative comments.
If you want to get fed, if you want to survive at all, you better shut up, slap on a smile and act like this world is perfect.
Better yet, don't act, really believe it. The happiest cotton picking slave was the one who wasn't just putting on an act when he slapped that smile on around the master. The happiest ones were the ones who convinced themselves that they really were inferior, that they needed white slave masters and that his personal master was a great man who only whipped him because he had to and that this was truly the best of all possible worlds.