Most news sources have pretty strict guidelines for letter submissions. Usually letters need to be very concise—often less than 200 words. You should go the opinion section of your newspaper’s website and see what their specific guidelines are.
In general, you should:
- Keep your letter short and focused on the subject
- Try to make just one point in your letter
- Make it timely: send your letter shortly after that news source covers the topic
- Refute or support something specific you saw in that paper
- Support your facts
The Fairness and Accuracy in Reporting website is a great resource for tips on communicating with journalists and editors.