Decide who you are writing the letter to. Perhaps you are writing a letter to a friend or a submission to a publication. With all creative fiction and nonfiction writing, you should always keep the intended audience in mind when developing the piece.
Brainstorm and outline what you would like to say in your letter. Casual letters are often exercises in free writing, but for this letter, planning will help guide the body of your letter. While brainstorming, consider your theories on writing and language and what you want to say about them.
Speak to your own personal experience, while finding inspiration from others. To find inspiration, look for meaningful quotes or written work that has helped you develop your understanding of the writing process. It is not necessary to say "I believe" or "I feel" throughout. Instead, develop your theories about writing throughout the letter as personal expression.
Format your letter according to the level of formality. If it is to a friend, a simple "Dear Bill" greeting followed by a comma is sufficient. It will also not be necessary to write a return or contact address. Dating is still relevant. If the letter is more formal (for instance, if it will be read by a review board or in an academic sense) use a more formal business letter format. Include a return address, contact name, date, contact address and a formal greeting such as "Dear Mr. Jones" followed by a colon. A business letter is not indented.
Open your letter with an introductory paragraph that states who you are and why you are writing this letter. Much the beginning of a research paper, this opening paragraph should also contain your thesis statement. Feel free to use literary devices such as simile, metaphor, alliteration and allusion where needed to strengthen the piece. Your technique should be apparent to the reader in the introduction and throughout the body of the letter.
Fill in your letter with supporting arguments. Develop what you want the reader to understand about writing, and then give support, perhaps with quotes, writing examples or historical references that can defend your argument.
Keep the tone of your letter focused on the intended reader. If it is a personal friend, draw on shared experiences that can help communicate your topic. If the letter is more formal, write in a larger scale about the role of writing or your chosen subject matter.
Write a conclusion paragraph that sums up your argument about writing. If the letter is meant to be persuasive, your conclusion should be a call to action. Leave the reader with a satisfying close, but keep her thinking about the subject matter. Follow with a closing phrase, such as "sincerely" and sign.