When you're happy with your CV, it's time to dig out your very best writing skills and write a covering letter. Here, you have to sell yourself as the best candidate for the job in question.
Adapt your letter to suit the job
Just as when you compile your CV, it's important to adapt your letter to suit the job you're applying for. You can propably not use the same letter for several applications, keep in mind what position you are applying and focus on the skills needed for that specific job.
Your covering letter is your opportunity to explain the information you've listed in your CV and to tell the person recruiting why you'd be perfect for the job in question. Remember to describe yourself just as you are, in both your CV and your covering letter. If the information is straggly, you'll come across as confused.
Strike just the right balance between personal and professional
In your covering letter, you can be a bit more personal than you are in your CV. Your letter still has to present you as the perfect person for the job, so don't focus too much on your personal interests. And even though you don't need to be quite as formal as in your CV, it's important to use correct language. Remember that what works in text messages to your mates isn't necessarily the right tone for your job application.
Proofread your application and eliminate any careless errors
Before you send off your application, it's important for you or someone you know to proofread it thoroughly in order to eliminate any spelling errors or other careless mistakes.