Example of a letter to your legislator
This letter is on a bill that was being passed in Senate. It is a perfect example of what a letter to your legislator should look like.
Please keep in mind, that legislators DO listen to their constituents. Letters should be persuasively written with a clear thesis as to how you want your legislator to respond to an event, vote on a bill, or react to a court decision. You letter should not be a reaction to something they did. After all, they can't do much to undo something they did.
Example of a letter to your editor
Letters to the editor should be written to the EDITOR or readership of the paper. If you are writing it to your editor, it will most likely be a reaction to something that appeared in the paper or an issue. For example, if the paper printed an article about abortion that you didn't agree with write back with your opinion. If you are writing to the readership, it should be persuasively written to encourage them to action or to change their mind. Here is an example of the latter that I found in my local paper: http://www.loudountimesmirror.com/letter/1533/.
Every newspaper has a section for these. Read the ones in your paper to get a grasp for what it should look like. It is important to remember who your audience is (other local citizens) and who it is not (your legislators). Also keep them short, newspapers have limited space, respect that.