Letter Paragraphs: Professional letter paragraphs should be relatively concise. The first paragraph may include a brief friendly opening and a concise explanation of your reason for writing. The second paragraph (and any subsequent paragraphs) should expand upon your reason for writing. The final paragraph should restate your reason for writing and, if applicable, state your plan of action (or request some type of action be taken by the reader).
Not only does this mean that you should focus on neutrality in your letter’s appearance (avoiding the use of colorful paper, brash logo designs, and artistic fonts), but it also means that you should employ a very low_key, unnuanced, and professional closing phrase. The best_case scenario is that the hiring manager, colleague, or connection won't even notice the closing.