State immediately why you are qualified and what makes you stand out from the other job applicants. Don't drone on with irrelevant facts or useless fluff in the first paragraph. Your reader might never get to the "good stuff" further down.
Keep the tone professional.
Written correspondence requires more formality than everyday speech. Be courteous. Don't use abbreviations or slang terms: "I've worked in LA (abbreviation) five years ago and it would be really cool (slang) to work in California again." Unless you're a professional comedian applying for a stand-up gig, don't joke or try to be funny. You want the employer to know you will take the job seriously.
Be clear, not clever.
You may think you'll sound intelligent if you use large vocabulary words and lots of lengthy sentences
Don't be afraid of action verbs.
Liven up your writing by using lots of action verbs to describe your career. Words like implemented, achieved, developed and created convey a sense of accomplishment.
Customize each letter you write.
Whatever you do, don't use a form letter that sounds as if you mailed it to 100 employers. Always take the time to customize each letter for a particular position or company. If you send an obvious form letter, you'll look like someone who doesn't care what job you get.
Use the active voice.
The active voice takes responsibility. The passive voice, however, passes the buck. For example, "I accomplished this" sounds more direct than "it was accomplished." Here is an example of a passive voice sentence: "Accounting services and financial advice were provided for several clients over a period of three years." Try the active voice instead: "As an accountant and financial advisor for the past three years, I've worked with diverse clientele." Whenever possible, choose the active voice over the passive voice. It will give your writing more punch.
Use bullet points.
Highlight your greatest strengths and biggest career accomplishments by setting them off with bullet points in the second or third paragraphs. By using bullet points, you'll attract the reader's attention to your best achievements, rather than letting them get lost in the text.
Embrace the power of the P.S.
Marketing studies have shown that most people will read the P.S. on a sales letter. Use this device to emphasize an important point: "P.S. I was recently honored at an annual corporate-wide meeting for perfect attendance." Hint: If the P.S. is handwritten, there's an even greater likelihood that it will be read.
Check your spelling and grammar.
We can't stress this enough: Spelling and grammatical errors are not acceptable! Use reference books if you're not sure about something. Check all spelling carefully and don't rely on a computerized spell-check as your sole means of proofreading. Even computers make mistakes. Proofread your letter at least twice and ask a friend to take a look at it.