When you are creating slides for your presentation, don't cram them full of everything you know about the topic. The slides are there to support your presentation, not replace you or replicate your brain.
Focus on Your Message
Just because you know all the details doesn't mean that you have to include them in your slides. Instead, focus on your message – the one thing you want the audience to take away from your presentation – and include only the specific details that will help you convey your message to this audience. Keep everything else in your brain or your notes to answer questions.
Good Slides Take Time
In order to create slides that are clear, focused, easy to understand and supportive of your message, you have to plan ahead and ensure you have enough preparation time.
Use Phrases or Images
Don't copy-paste entire paragraphs of text or full Excel spreadsheets into your slides. One of two things will happen; either a) the audience won't be able to read the small font so they will be frustrated or b) they will read it to themselves faster than you can read it aloud to them, which will leave them wondering why they needed you to present in the first place. Neither is a good way for you to engage your audience.
Instead, use short phrases or high-quality images that are easy to read, even from the back of the room. Then you can provide the voiceover that builds on the information in the slide.
Why Do You Need This Slide?
For each slide, ask yourself: What is the point of this slide? How is this slide related to the slide before it and the slide after it? If you can't answer these questions, edit the slide or cut it out of your presentation.
Keep Extra Info to Answer Questions
Be open to audience questions (while also being mindful of your time limit). Use all the extra information that you didn't include in your slides to answer the questions, which will demonstrate your command of the topic.
The next time you have to give a presentation using slides, remember that the slides just play a supporting role - make sure they do their job by making them clear, focused and supportive of your message.