Before a critical presentation, the best thing you can do is rehearse – a lot. That doesn’t mean you need to memorize every line (which will make you sound too rehearsed). Your goal should be to feel confident in what you’re saying while leaving room for spontaneity.
The trick is to spend extra time practicing the beginning and the end of your talk, including your first and last slides. The introduction sets the stage for your message and gives your audience a reason to care. Your conclusion determines which ideas people will walk away with. If you nail these two sections of the talk, you’ll probably do well no matter what happens.
You should also repeatedly practice any sections that have complex or technical content. While you rehearse, consider recording yourself on your phone; play it back to watch for distracting habits (fidgeting, avoiding eye contact) and areas where you seem unsure of yourself. Rehearse those sections a few more times.