Once you’ve outlined your speech and lined up some solid evidence to back up your ideas, it’s time to put all the pieces together. Whether you plan to write out your speech word for word or just speak from notes, you need to have a clear idea of what you want to say — the actual words, not just the ideas.
It is generally recommended not to have everything you want to say written down but rather a series of prompts. If you appear to be reading from a script, then there is less chance of you getting your point across with the power that you want it to have.
Nonetheless, you should refrain from improvising too much as there are clear disadvantages to this process, not least of them the fact that this is filled with risks such as momentarily being lost for words.
This makes you appear less competent, and people will be less likely to take you seriously. The general impression is that you should have in mind the body of what you want to say, and any additions which occur to you can always be included. Therefore, you do not have to worry about deviating from a pre-written speech, while also avoiding the dangers of having nothing to say.