Similar to preparing for an interview, examine the job posting you're applying for and pick out the key responsibilities and skills. (blog.simplyhired.com)
No matter what kind of post you are applying for, it is always best to double check your grammar. (wolfgangcareercoaching.com)
The cover letter should give a clear picture for which post you are applying for and a brief summary of your resume. (bestcoverletters.com)