This course is available as a two day seminar, as also as a correspondence course and over the Internet. Writing is a communication skill. The most important communication skill in business.
Clear writing means clear thinking.
When you are face to face with a customer or a colleague, you can always retrieve your foot if you put it in your mouth and sort out any misunderstanding. Not so with writing. There it is, carved in stone for posterity. You need writing skills to write clear reports, to communicate clearly by memos and E-mail and to sell to your customers. Poor writing gives a bad impression.