It helps to have a persuasive speech outline, filled with memorable anecdotes that you can relay to your audience. But once written the next step is to deliver that speech.
Strong vital presentations require a strong vital speech opening. Your introduction is like the headline on a newspaper story. It must grab your audience's attention. Normally, this is done with a strong voice, and some sort of hook. A question appropriate to your audience and your topic is one good way to plan a speech opening. An outlandish statement, a provocative quote, and even a carefully practiced joke that is directly relevant to the topic can do the trick.
When doing your presentation practice, it is a good idea to memorize your opening. This both helps you overcome any initial jitters, and makes it easier for you to project yourself with a good clear voice.
Since your speech is about something, you want it to end with a call to action of some sort. This is the payoff for good speeches. You have shared information, and now you are asking for the sale. Next to getting your audiences attention, which is a prerequisite, this is the most important part of your speech, and it too should be memorized.
The middle, the body of your speech, need not be memorized and in most case shouldn't be. Rather you should memorize your speech outline, and remember the key stories you are going to tell to illustrate each point you are making. Your audience will remember your stories a lot longer than any facts or figures. And your speech again is about your audience, not you.
Presentation practice then focuses on the memorizing of two small but vital speech parts, and then playing around with different ways of telling the stories in the middle. Most people start at the beginning, and then the first part of the body, and then go back and do the middle the first part and then the second part of the body and then back again, and work their way through to the end. This makes sense, but if you run out of time and don't quite get that ending down, your presentation will suffer. Thus it is again a good idea to memorize that final call to action up front in the speech practice sessions. Besides, it helps inform your conscious and sub conscious as to what the middle of the speech is building toward.
While it is always good to practice your presentation aloud in front of a mirror or ideally a small supportive audience, there is nothing wrong with doing it quietly in your head. Over and over again. And don't worry about it being different each time. In fact it is good to try a variety of different ways to say the same thing. If you have your speech opening down pat, as well as your conclusion, and know the topic and each of the points that fill the middle, you will find that your subconscious mind will guide you to the better choices while you are giving your presentation, and that they will flow together better.
Good presentations require presentation practice. Just keep in mind the bookends should be done by heart, the middle by practiced intuition.