Your letter has the best chance of being published if it is a reaction to a story in the paper or a big story in your community. Respond as quickly as you can, and as clearly as you can making a compelling argument or point.
Read the letters to the editor page of your local newspaper regularly, you will learn how to develop an effective letter-writing style that appeals to that specific outlet, and you will see what some of their “hot topics” are. You will also see if someone has already addressed the point you are trying to make.
Though your letter should be interesting and stand out, you should refrain from insulting anyone in the process. There are plenty of ways to make a point without burning bridges. Keep it short and concise (150-200 words). When necessary, the paper will take the liberty to shorten your letter to suit its format; the more it has to cut, the less control you have of what gets printed. Lead with your most important information and be sure to read it over a few times to be sure it makes sense. Have a friend or colleague read it as well to be sure it makes sense to the outside reader.
Focus on one main point and make a compelling case, have laser focus, and don’t let your thoughts go off on tangents that have nothing to do with the main issue you are writing in about.
Don't write too often, you won’t to get the reputation of someone who has relevant opinions and useful information to share, not someone who never tires of the sound of her own voice, or the look of her own words on paper. Stay away from being the “girl who cried wolf” and instead speak out when something strikes a chord with you or your business.
Put your full name at the bottom, and include a phone number for verification purposes. Also include your title and company in order to bring awareness to your brand as well.
Remember that as we are in the age of the Internet, anything you say can and will be used against you (or at least Googled) in the future, so choose your words wisely!