How To Write A Professional Letter Of Instruction . Headers have the date and. A letter of instruction is any letter written giving another party an order or guidance with something. 13+ Sample Letter of Instruction Templates PDF, DOC Free & Premium from www.template.net Starting to write 1 since this will usually be about getting somebody else to complete a task, you need to be clear and specific with what you want. However, it is important to ensure this document. You will be able to modify it.