Like any good piece of writing, your cover letter should begin with a hook to grab your reader's attention. In your introduction, be sure to define your purpose. Plan to include at least three organized paragraphs in your letter - an intro, middle, and closing paragraph to outline your thoughts. Make sure you mention which position you're applying for and why you're interested in the position and company - if someone referred you to the position, mention it here. Your cover letter should take up the majority of your page, but should never be longer than one page in length.
Feel free to include more than one body paragraph, but make sure you focus on key points that are relevant to the job you're applying for. This is your opportunity to really market yourself and explain your past experiences in more detail. Talk about your previous job responsibilities, projects you worked on, and what kind of impact you had on the company's success.
Your body paragraph(s) is also a great place to elaborate on any awards or accomplishments you achieved, as well as unique achievements that were above and beyond your job requirements. Choose things that will set you apart from other candidates and show your capabilities: perhaps you've written a book, built a website, grown a podcast, talked at workshops, or learned a new skill on the side.
Before you sign off, there are a couple of things to keep in mind. Make sure you reiterate why you're interested in the position, summarize your content, and restate the qualifications you have that would make you a perfect fit for the position. Be careful not to make your closing section seem unnecessary. Remember, every word should have a purpose and be thoughtfully laid out on your page. Don't forget to include a call to action and invite the hiring manager to follow up with you, or set a time when you will contact them.