The following guidelines will help you meet a busy editor's criteria, and increase the odds that the editor will choose your letter. Have a clear viewpoint, and present only those facts that support it. Be temperate, factual and fair. Editors are resistant to vitriol and name calling. Use short sentences that get the point across.
Structure Keep the letter short.
Use the first paragraph to state the subject and refer to the article you are responding to, if any. Include the date of the article. The second paragraph should summarize your reason for writing the letter. Treat this as your argument conclusion, and make that conclusion as vivid and attention-drawing as possible. Then present any supporting facts, statistics, anecdotes or samples.