The same story was with me a few months ago. I was simply stdarn on that letter and could not make up my mind what is next. Check out some really useful hint how to write such a letter, this page, and know for sure with a full step-by-step guide on writing such letters. Cheers
One solution is to make your letter as concise as possible so that it doesn’t look like a daunting reading project. Be as brief as you can and make sure your letter has a pleasing amount of white space. Keep your paragraphs short and include no more than 4-5 paragraphs. Cover letters sent electronically in the body of an e-mail message should be especially brief.