Mistake 1: Typos
Employers see them as a lack of detail-orientation, as a failure to care about quality.
Mistake 2: Length
A good suggestion is one page of resume for every ten years of work experience.
Mistake 3: Formatting
Keep your resume clean and legible. Suggested specifications: Ten point font size and half-inch margins minimum. Consistent spacing between lines, columns aligned, and have your name and contact information on every page.
Mistake 4: Confidential information
Don't share trade secrets etc of your previous employers / clients.
Mistake 5: Lies
Things people lie about: Their degrees, how long they were at companies, how big their teams were, and their performance / results.
Remember: Not only can your lies be found out in the age of the internet, your lies of today can hurt you further down your career.