When I have not prepared a presentation well enough, and/or made last minute changes to the deck, I find myself skipping a slide during a live presentation. Click-click, when you see a difficult slide coming up in presenter view (more about PowerPoint presenter view here).
Where do you need to practice most?
The opening of the presentation, and not only because here you are likely to be a bit nervous at this stage of your talk. It is here, where you usually talk about yourself as an introduction. You know the content of this section very well (hey, it is about you) and you do not bother rehearsing. So you are on stage, you go blah, blah, blah, and a feeling starts creeping in. This section takes a long time. Is all this detail about me really interesting to the audience. How should I have told the story about myself in such a way that it sets up the rest of the presentation correctly? It is hard to talk about yourself, better practice it...
Visual mental placeholders. These are slides that are great to talk around in a one-on-one meeting. You probably have used them a lot. You know them inside out, and hence do not bother to practice them. But when you are on stage, you realize that you do not have a good sequential story in your mind to talk a larger audience through this slide.
Bad slides. You will discover them when you practice. DELETE.