You may have heard the advice that you should practice your talk to the point where you have every single line down cold.
The problem is, that takes a crazy amount of time. Moreover, many talks aren’t monologues like at TED, but involve some degree of audience interaction. You need some flexibility in order to respond effectively to whatever happens in the room.
The solution I recommend is what I call the Landing Pad method. The idea is that you do a word-for-word script only for the most important parts of your talk – the moments you really need to get right. Those moments are your landing pads.
The landing pads are effectively ‘safe havens’: You can be free to extemporize somewhat around them because you know you can always return to it and ‘land’ that segment of the talk.
To be clear, you should still practice the other parts of your talk too. I’m not advocating total improvisation. It’s just that you can practice those parts much more loosely.
In your talk, both your start and your ending should be scripted. Beyond that, I tend to have maybe two to three landing pads per module (meaning per every 6-8 minutes).