Your covering letter may well be the first thing potential employers see. It provides additional information on your skills, knowledge and experience and gives you the opportunity to highlight why you're the right applicant for the job. A covering letter is vital to any job application and should always be sent, regardless of whether the job advert requests one. 

Your covering letter allows you to go into more depth than your CV itself. Often it's difficult to make your skills and experience stand out from all the other candidates applying for the role, who may well have the same skills set as you. Your covering letter gives you the chance to show your passion for the job, and allows you to reveal aspects of your personality to help you stand out from the crowd. 

In today's job market there may well be a hundred people applying for any one job, therefore employers have a lot of applications to read through. Keep your covering letter to the point; ensure it isn't too long, it's punchy and is interesting to read- you don't want to fall at the first hurdle. Always tailor your covering letter to the job you are applying for; do your research and immerse yourself in their language. Ensure your first sentence is catchy and grabs the reader's attention. Be bold and brave in your choice of language and don't state the obvious, such as the job you are applying for- they already know this! 

Include your achievements in previous roles, to highlight why you would be an asset to their company. Show how these have developed you professionally, and have helped you to obtain the skills needed to be the perfect candidate for their job. Be sure to include examples of these achievements from the work place.

Make it clear to the reader why it is you want this job, and why you feel you are right for the role. Make sure you demonstrate this, perhaps by taking something from their job description and showing with examples how you have handled this previously.  

Ultimately your covering letter is the best place to show off your skills, grab the employers attention and convince them you are the best candidate for their job. Don't be tempted to send off generic covering letters for multiple roles- this won't make you stand out and it will be obvious to any potential employer. Make sure your covering letter has impact, includes examples, uses the language of the potential employer and shows how you would be an asset to the team. 

By taking the time to create a decent covering letter, it shows any potential employer you're serious about their job- you've put the effort into the application.