How To Write A Professional Letter To Convince . Be brief and use clear, uncluttered sentences. There is a standard format for writing professional letters, including page margins , font selection, paragraph spacing, contact information, introduction and closing sections, and your signature. Persuasive Letter from www.slideshare.net How do i write a “convince your boss” letter? State your purpose for the proposal. Here are the steps you can take to write a professional letter: