According to subj:

When asked to identify the biggest mistakes recent college graduates make during the application and interview process, employers reported the following:

• Acting bored or cocky - 63 percent
• Not dressing appropriately - 61 percent
• Coming to the interview with no knowledge of the company - 58 percent
• Not turning off cell phones or electronic devices - 50 percent
• Not asking good questions during the interview - 49 percent
• Asking what the pay is before the company considered them for the job - 38 percent
• Spamming employers with the same resume and/or cover letter - 21 percent
• Failure to remove unprofessional photos/content on social networking pages, Web pages, blogs, etc. - 19 percent
• Not sending a thank you note after the interview - 12 percent