A covering letter is a vital tool during the application process because employers often read the cover letter before the CV. If this is the case then your covering letter needs to be equally as impressive as your CV. A covering letter is a letter of introduction that highlights your main skills and your suitability for the role that you are applying for. From personal experience I can tell you that few employers will seriously consider a CV that is not accompanied by a covering letter.
My advice is whenever possible; send a covering letter with your CV because it demonstrates your level of motivation, commitment and relevant skills. There are a number of things to consider before you start writing your covering letter. Remember to always tailor your covering letter to the advertised role/position. Try to show evidence that you have researched the role, company or the industry. Finally, illustrate why you are attracted to the role and what your unique selling points are. If you can address all these areas, then you are well on your way to producing a very high standard covering letter.