Writing your cover letter:
Ideally, your cover letter should fit on one page
Wherever possible, address the letter to a specific person
First, mind map or make a list of the key points you want to include in your letter. Add sub-branches to your mind map or sub-points to your list as ideas come to you
Arrange your points in a logical order
You can now start to write your letter, building your sentences around the points you have identified, in three or four paragraphs
① Say why the job interests you.
② Match your profile to the job ad by describing your experience and/or two or three skills that demonstrate you are an ideal candidate. Give specific examples, but don't repeat the content of your CV word for word.
③ Highlight relevant achievements.
Then edit your letter, cutting out any unnecessary words that add nothing to the meaning. It's crucial to be specific and concise.
Proofread your letter carefully to make sure it is well expressed, accurate in grammar and spelling, and that you have addressed the selection criteria in the job ad. If at all possible, get someone else to proof your letter (and CV) too.
You could also mention:
where you saw the job ad
dates when you are available for interview
anything that demonstrates your interest in the organisation and what they do (eg research you've conducted, articles read, website visited)