It should emphasise the most important and relevant points about your experience, skills and education. Certain words are used frequently by recruiters in their job descriptions. You should study recruiters' advertisements and job descriptions and use these words in your CV and covering letter. The most powerful words are verbs. If, for example, you are applying for a management post, you should use as many management skills power words as possible - and use them in the active form, not passive.
Numbers are alive and powerful.
They create vivid images in our minds. General statements are easy to ignore. Be specific and use numbers when describing your duties and achievements. Don't talk about 'managing a major turnover'. Don't talk about 'extensive teaching experience'.