Never complain about your previous boss or company. This was the second most common interview mistake cited in the CareerBuilder survey. You may have well-justified complaints about how you were treated or how your previous company operated, but keep them to yourself. Employers don't want to hire disgruntled workers.
You shouldn't speak badly about your former colleagues, either. You want to show that you are eager to fit in -- not a person looking to assign blame. Don't talk about the bad economy or the sorry state of the industry. You also shouldn't discuss personal problems like financial worries or family complications.
When you talk about previous jobs, put the emphasis on solutions and accomplishments, not on difficulties and frustrations. If asked why you left your former company, put a positive spin on it: You might say you're looking for greater opportunity or new challenges.