Misspellings and grammatical errors are killers. Spell check then proofread by placing a finger on each word and then have your document reviewed by a career coach or a friend or family member. It's hard to catch your own mistakes, so having someone else read your resume will help. Reading it out loud is another way to catch mistakes.
Not including keywords that match the job posting. Your resume should include the same keywords which appear in the job listing. If your resume doesn't have the right keywords, it likely won't get noticed because you won't appear to be a fit for the job.
An outdated resume will make you look obsolete. Your resume should be updated for every job for which you apply.
Be sure to update your skills section and your work history. Be sure your computer skills and any other skills are listed and updated.
Including too much information. Don't tell your readers everything about each job. Focus on the highlights - keep your document to 1 - 2 pages in cases outside of academic and research settings. Use formatting techniques like bullets and short paragraphs to enhance readability. Limit your resume to the last 10 - 15 years of work
experience. You don't need to include everything you ever did.
Writing a resume objective which doesn't match the job. Avoid using an objective statement which doesn't correspond well with the focus of the target job. Many job seekers now leave an objective off their resume or use a profile instead. Either way, make sure it underscores your interest in the type of work for which you are applying.
Including a career summary that doesn't match the job requirements. Don't use a mismatched summary of qualifications at the top of your resume. Your key assets in the summary should match many of the key job requirements or else leave it off.
Writing position descriptions that don't show what you accomplished. Avoid job descriptions which simply list your duties or responsibilities. Instead write active statements which showcase relevant skills and accomplishments. Make sure the employer can easily see how you added value in your role.
Leading your paragraphs with mundane or irrelevant duties. Start with the hardest hitting statement which show you have key skills related to the job at hand. Otherwise your reader might just skim by that description.
Not quantifying accomplishments. Avoid empty self-congratulatory phrases. Quantify accomplishments or provide other concrete evidence to support your assertions.
Being too modest. Share any awards or recognition you have received in a matter-of-fact manner i.e. "Promoted to associate director after increasing annual donations by 25%."