The first step in writing a college-level persuasive letter is to target your audience and know them well. You will want to establish how much they are likely to know on the subject to determine the approach your should take in your letter. Also, you will want to consider your audience's position on the subject. By doing so, you can anticipate any potential objections they may have to your arguments. Lastly, you will be able to identify what the reader has to gain from your request so you can use it to strengthen your arguments.
Establish for your reader the issue or a problem. To do this, you should research the issue at hand thoroughly and consider every angle and argument tactic. By having a firm grasp on the issue and educating yourself on it, you will be better able to convince your reader that you are an authority on the matter. This will convince your reader that you are worth listening to. Once you have established the problem, make a firm statement declaring your position.
Provide your audience with evidence to support your claims. You should have many details that can support your argument, but the way you present them can affect the success of your letter. You should start with strong evidence, follow it up with the weaker of your evidence, and then end with another strong piece of evidence. This way, your first and last impressions will be memorable.
Format your letter correctly. Whether it is a letter for academics or a letter you actually intend to use, you will want to format the letter like a business letter. Your heading should consist of both your address and the address of your reader, followed by the date and a salutation. If you can, address your audience directly by name or title. Otherwise, you can use "To Whom It May Concern." End your letter with "Sincerely."