I have been on the swim team since I was a little girl. . Close the letter with a polite and professional conclusion, such as "Yours sincerely" or "Best regards. " Sign your name below the closing, and consider. Close the letter with a polite and professional conclusion, such as "Yours sincerely" or "Best regards. " Sign your name below the closing, and consider. We were up against our biggest competitor of the season, and I was certain.