The language used in the sales letter format should be simple, and suited to your trade. Complicated or complex writing leaves the reader confused and unlikely to read your letter or take action and buy. When a letter writer includes any bonuses, they should be supported with the word "free." For example: "FREE article submission with every SEO article!"
The letter format should use an appealing font. Maintain uniformity of font and size all through the body of the letter. At the same time, you should create headlines and titles to seem different by simply increasing the font size slightly. Capital or bold letters should be done with care so that reading continues to be smooth. The art of sales writing is time consuming. You could refer to a few sample letters to see how they have made good use of fonts to give a perfect finish.