We'll detail everything you need to know about how to invite a guest speaker, from the earliest planning stages to drafting a formal speaker invitation letter. Discover considerations, best practices, and essential elements of a wellstructured speaker invitation letter.1 Formatting the Letter. Format the invitation as you would a formal business letter. To provide the QUICKEST turnaround for this, please fill in the form below and we should be able to get back to you within 48 hours.