Hiring managers and recruiters receive hundreds, if not thousands, of cover letters and resumes every day. With this in mind, your goal is to stand out from the crowd – in a good way. Think of your cover letter as your 30 second elevator speech. You need to make an excellent impression, quickly. Knowing what not to say in your cover letter will ensure your resume does not get tossed into the recruiter's “circular” file.
Do not include information about medical conditions. Aside from asking if you are able to do the job or need any type of assistance, employers are unable to inquire about your personal medical history. Revealing any type of medical condition in your cover letter will put the employer in the unspoken and uncomfortable position of focusing on potential discrimination suits rather than your qualifications for the job. Unless there is a compelling reason for it, focus on your skills rather than sharing health related information.
Keep the language simple. While you may be prone to flowery speech or enjoy showing off your extensive vocabulary, keep it simple. Big words will not impress a recruiter, your ability to describe your potential value to the company will. Go for the middle ground, don’t make it overly complicated nor insult the reader by making it too elementary.
Watch your words. You only have so much space in your cover letter. Use it for details, not fillers. Don’t use five words when one or two will get the same point across. Avoid old-fashion speech. Also avoid using slang unless the position warrants it.
Do not mention your reasons for leaving a prior employer. This is the time for you to talk about your accomplishments and other “value-added” information. There will be plenty of time to discuss the reasons for your job hunt later during the interview.
Everyone likes a professional looking letter. Do not, however, use your current company's letterhead for your personal cover letter. Instead of looking professional, you will look cheap, even worse - a thief stealing company assets.
Remember that recruiters only have so much time to scan each cover letter to pick out the details which they feel will best match the position. They do not have time to read your life history, therefore, a cover letter should be no longer than one page. Any information on the second page will mostly likely be ignored.
Think of the cover letter as your 30 second elevator speech. Knowing what not to put in your cover letter will help you to get past the initial screening for almost any position.