You already know you don't want to read a speech verbatim from a screen or notes. You could memorise the speech word-for-word, but not everyone is able to do that -- and it isn't natural. Instead, use "key images" to remember your important points.
A helpful infographic from Essay Tigers explains that you should find a visual image for each part of your speech. This is just like remembering someone's name with a visual hook, but with your speech.
Once you've got those images in place, you then memorize the details of the image instead of the exact words you'll say. Though obviously, if your speech is just facts and figures, this tip won't work as well.
How to Memorize a Speech [Infographic] [Essay Tigers]