Type your letter with formal letter style. This includes including your address, skipping one line and noting the date, and then skipping a line and inserting the casting director's name and address. Be sure to address the letter to the proper person, not the agency. Skip a line and add the salutation, such as "Dear Mr. Smith," followed by a colon and another blank line. Begin your first paragraph, and include a blank line between each paragraph. Each line should be single-spaced and flush left. Use a simple font, like Times New Roman, 12 point, or Helvetica, 10 or 12 point.
Double-check the casting director's name and ensure correct spelling. If you don't make extra effort in this area and misspell her name, the casting director is less likely to trust you to do the work necessary for a film, TV or commercial part.
Introduce yourself in the first paragraph with any personal connection you may have. For instance, if you met the casting director's brother at a party who suggested you contact him, write that in your letter.
List no more than three parts in which you have been cast in the second paragraph. You may explain that you recently finished a television series pilot and are appearing in an off-Broadway play. If you are cast in a stage play, offer the casting director tickets to see the performance. Ensure you have that authority before you offer the tickets.
Close the letter simply. Thank the casting director for her time and give her a contact number where you can be reached. Skip a line and give the closing, such as "Kind regards," or "Sincerely," and then hit the "Return" four times and type your name. Sign your name in ink in the space where you returned four times, above your typed name.