1. A history of job-hopping. If you have a history of moving quickly from one job to the next without staying very long, employers will wonder whether you get bored easily or can't keep a job. If you do have good reasons for the job changes (such as having a spouse in the military), make sure to fill in employers upfront so they don't draw wrong conclusions.
2. Grammatical or spelling mistakes. Mistakes can get your resume immediately tossed, because they convey to an employer that you don't pay attention to detail. Employers assume that you've polished your resume more than you will most documents, so if you have mistakes in it, they assume your work will have even more errors.
3. Bad writing. Even for jobs that don't require flawless writing, employers still want to see evidence that you can communicate well. If you don't write clearly and concisely, they'll worry about how you'll communicate once on the job—and many will take your resume-writing quality as a shortcut to drawing conclusions about your intelligence.
4. Overly aggrandized self-descriptions. Hiring managers generally frown on language like "visionary thinker," "creative innovator" or "respected leader" because these are the sorts of things that others can say about you, but you can't say credibly about yourself. Putting them on your resume signals that you're either naive, arrogant or both. Stick to objective experience and accomplishments only.
5. Lack of evidence of achievement. If your resume lists nothing but your job duties at each job—rather than what you achieved there—you'll signal that you never did more than the basic requirements. Hiring managers are looking for candidates with a track record of achievement, not meeting minimum requirements, but going above and beyond and accomplishing things that an average candidate wouldn't.
6. No overarching theme to your career choices. If you've moved from one unrelated job to the next, without a clear pattern, employers will be skeptical about your commitment to the roles you're applying for now. Most employers want to be able to scan your resume and get a quick understanding of how you've progressed within one or two fields, rather than trying to work out how you've moved from tech writer to salesperson to nurse's assistant to video editor.
7. Lack of professionalism. If your resume includes information about your spouse and children, or other information unrelated to your qualifications as a candidate, most employers will conclude that you're naive at best and unprofessional at worst.
8. Large gaps between jobs. When employers see gaps of unemployment, they wonder what happened during that time. Did you leave the previous job with nothing lined up, and if so, why? Were you working somewhere that you've deliberately left off your resume, and if so, what are you hiding? Gaps raise questions that you don't want on a hiring manager's mind.
Alison Green writes the popular Ask a Manager blog, where she dispenses advice on career, job search, and management issues. She's also the co-author of Managing to Change the World: The Nonprofit Manager's Guide to Getting Results, and former chief of staff of a successful nonprofit organization, where she oversaw day-to-day staff management, hiring, firing, and employee development.