Two pieces of advice on preparing a speech.
1) Writing a speech verbatim (word for word what you plan to say and then trying to memorize it) is not recommended. There are exceptions when you want the time to come out very precise and you will largely be reading it (see the nineth speech of the manual, which is a particularly dreaded speech). The problem is that if you try to memorize the entire speech and then lose you place it is very hard to get back into the flow. And a memorized speech sounds memorized; it lacks the flow and spontaneity that connects with an audience. (See preparing a written speech)
2)When I was a freshman in college I rather logically took the course: required freshman course in English. While I don't remember much of the course there is one thing that I do remember and which convinces me I had a good professor. The professor loved the following story (which I have been passing on to most people I meet). At some large university, during exam time, a young man was wishing good luck to a friend who was about to take an exam and was still there when they locked the doors and began the exam. Unable to leave (because the doors were locked for the exam) he had no choice but to take the exam. It wasn't a course he had taken or knew anything about. He was completely unprepared and the test consisted of a single very long essay question about a book (which the young man hadn't read) with a long title. Based solely on the question and the title of the book the young man tore the last page out of the blue book, made an outline of his proposed answer and proceeded to write an essay answer.
The next day, when the grading was done, the professor gathered his colleagues and met in a secret, closed door session to determine what had happened. The young man had, without attending the class or knowing the material, received an A for the final! The reason was that his essay had been so well organized. This is a procedure my professor strongly recommend and one of the two most important things I learned in college.
The reason I have written out this rather long story is because I want to suggest that making an outline for a speech is a very good procedure. Further, I will pass on that my notes for a speech usually consist of a key word or two for each topic I want to cover, in the order I want to cover them. (There have been exceptions, such as the time my notes consisted of a single word, an odd sounding name that I was afraid of forgetting).
With such an outline, written on an index card held vertically in the palm of the hand, where the audience won't be distracted by it, if you lose your place you can quickly check your list, find the next topic, and proceed.