Ask the person well in advance of the date you want him or her to speak. Some speakers are booked a year ahead of time, so make a list of two or three alternative people in case your first choice declines.
Write your letter of invitation on letterhead if you have it. If not, note your address, telephone number and the date. Follow this information with the inside address, which is the same as the one that goes on the envelope.
Begin with the salutation: the individual's title, surname, followed by a comma. An example of the layout is "Dear Professor Jones,".
Use the block business letter format. This is where all sentences start on the left-hand side of the page and you leave a space between paragraphs. Remember that when you change topics, you have to start a new paragraph.
State the purpose of your letter clearly. Something along the line of "I am writing to ask if you are available to address the annual meeting of the American Association of University Women, to be held at Western State College, on May 5th, 2011."
Indicate if there is an honorarium or stipend for speaking at the college function. If you are on a low budget, let your speaker know that in advance. After the speech, give her a small gift, such as a book, as a token of your appreciation.
Write a paragraph about why you are asking the person to speak. People always like to hear things about themselves so something along the line of, "I heard you speak at the teachers' conference at Brighton College last year and I was impressed with your honest approach to education."
End your letter by referring to your contact details and a date by which you need a reply. Thank the person for considering your invitation to speak.
Use a formal closing, such as "Sincerely,". Leave three or four spaces for your signature and then type in your name.
Leave your invitation letter for a day or two and then edit it for spelling or grammatical mistakes. It is also a good idea to ask a colleague with good editing skills to review the letter, as there may be something you missed. Be sure to sign the letter before you mail it.