Well, let me try to answer your question. According to my friend's experience, you need to "practice as many times as you can". My friend who's a very shy person, but wanted to make a breakthrough in public speech. So, about a month before the contest, he started to practice his speech at a empty classroom over and over again, even he recorded and checked which part should adjust. So, when the day finally comes, he already practiced for over thirty times, the content just like stamp in his mind. Due to his fully prepare, he won the speech. Wish you good luck!