Absolutely nothing beats the effectiveness of testing your presentation with a sample of your intended audience. Their perspective is exactly the perspective you need to consider as you improve your presentation's clarity, length, content, and design.
Here are three tips for how to test and improve your presentation.
Test with a sample of your target audience, not just friends.
This may not always be possible, but if there is any way for you to take a sample of your real intended audience to get feedback — do what you can to make it happen! Their feedback will be the most true and crucial to make your presentation resonate.
So, if your intended audience is potential customers for your sales deck, try to get a few potential customers to give you feedback on your first drafts.
If your intended audience is staff for a big company update, do a test with actual staff. What you're looking for is the genuine reaction of your intended audience: is your message clear? Do they have questions or resistance you didn't foresee? What do they think of the flow, length, and design?
Feedback meeting structure
Make the feedback meeting as least twice as long as your actual presentation.
You'll want to go through your entire presentation, start to finish, first, so your audience can see the whole thing without interruptions.
Then, go back through the presentation section by section, and get feedback on what worked and what didn't.
Don't ignore your critic's points
It's easy to justify your presentation decisions by thinking "that person doesn't know the context, so their feedback is irrelevant" or "that's just his personal opinion."
Instead, take the feedback you're getting to heart and think about if there are ways to improve your presentation to address some of the feedback you've heard. It's hard to absorb critical feedback on a project we've worked hard on, but the point of the exercise is to improve the presentation. Make sure, as you hear feedback, that you understand the intent behind it, so feel free to ask follow up questions yourself.
A great resource to learn more about the structure of great presentations is the book "Resonate" by Nancy Duarte.