Let's face it, recruiters (or employers) are smarter than we think. Big organizations pay a hefty salary to their HR department to filter out and sieve through hundreds and thousands of resumes. The idea is to build an organization with people of right mental aptitude. Most of top organizations believe strongly in a motto - "People are our greatest assets". Your cover letter goes a long way in capturing and retaining attention of these people whose main job is to recruit people and coordinate with workforce.
A well-written cover letter engages recruiter and pushes him to spend more time reading your detailed resume. Before you start off writing your cover letter, write down what you want to convey on a paper. Read it once, twice, thrice and then set off for a good start. Pack in as much power as you can, because it is these 400 or 500 words that can make difference.
Have these things on your mind before you start off writing:
Keep your sentences short and avoid using really long sentences because you don't want recruiter to read it twice to understand what you're trying to convey. Got point.? "Keep your sentences s-h-o-r-t."
Keep your language simple. "I take immense pleasure in applying for this esteemed position in this esteemed organization." Hell.! Your employer knows more about his organization than you do. So you can as well cut "false" praise. Maybe a subtle mention can do wonders. "I look forward to work with JK Industries".
Organize content of your cover letter into small paragraphs or bulleted points, not exceeding three paragraphs. Typically each paragraph can contain 3 or 4 sentences.
Do NOT use slang or spoken words like "Lookin' fo a kewl break into yo IT world".
Make sure your cover letter (and resume) is free from spelling or grammatical errors.
And most important: Deliver what employer is looking for.
So, what should you put in your cover letter?
Ask yourself two questions. One, why should employer choose you over others? And two, what can you give to company that others cant? Skills, yes. Proven experience, better.
A good way to start writing is with correct greeting phrase. If you know name of person you are addressing then you can start with 'Dear Ms. Stevenson' or 'Dear Mr. Washington'. Do not use their first names. A bad greeting would be 'Hi Jane' or 'Hello George'.
The first paragraph is to contain a reference. If this is a response to an advertisement or a vacancy listing, this is where you refer to get their attention. Alternatively you can put in a separate line mentioning your reference. (Ref: Your advertisement on Jobsite.com - Ref # 12345).