Just because you're a seasoned performer doesn't mean you'll automatically be glib and gracious. (Personally, I blew an acceptance speech a few years ago when I was inducted into my high school alma mater's hall of fame. Thanked everyone. Except my wife. Took me dozens of roses to make up for the guilt.)
One of my favorite speakers, Patricia Fripp, has a terrific article called "How Do You Accept an Award? Tips on How to Give an Acceptance Speech" that is filled with everything you need to knock it out of the park when you receive that Lifetime Achievement Award.