Your audience and objective guide your storyline
Don't Open PowerPoint!
It's tempting to go running straight into the creation of the slides. My advice is to let your brain think first; who am I presenting to? What do I want to achieve with this presentation? And what is the basic storyline I want to follow?
Take a few minutes to write down - who is the audience and what's on their mind? And what's my objective - what action do I want them to take after the presentation? If you get these things right, you'll find it so much easier to have a good story. These few minutes of time investment will speed up the process of building your story.
Here's a short video about how to assess the audience.
And here's another about being clear about your objective.