Ask most any speaker, and the most challenging aspects of their presentations are their audience's Final Destination - and their own presentations closing lines.
It's easy to get caught up in the Attention-Getting Opening, and the Point Proving Stories, and find ourselves at a loss when its time to wrap up. I think its an inner struggle we have between not wanting to repeat ourselves and thinking 'if they don't have it yet, they never will'!
Those last few lines you leave your audience with, however, can make or break your presentation, and are the difference between being Speaking and Delivering.
What's Your Message? Sounds like basic advice, but we often need the reminder. If we aren't clear on what we want the audience to leave with, how can our audience be?
Write the End First. Once you know your message, write the last few lines of your speech. Don't worry, you'll go back later and revise it, based on the rest of the speech. By having a clear and defined close to start with, though, you're less likely to stray from the message in your revise.
The End Determines the Rest. If your opening and supporting material doesn't lead to your ending, you'll know right away when the ending is predetermined. Be willing to part with even your favorite stories in favor of more appropriate material.
Practice, Practice. Yes, the first 30 seconds is important to have down to an exact science in your presentation, but so are the last 30 seconds. Don't risk flaming out as you reach the runway. Put the same work in on your conclusion as your opening.
Bonus Thought: The Pre-Close
Easily confused with the actual close, but comes just before. It's the minute or two you spend recapping, recalling, and referring to the points you've made and how they all work together.
Your pre-close should evoke the meanings of your points without needing to make each one of them a second time. Subtly combine your points to lead to the overall result - your final message - and your closing message will be the primary take home piece for your audience. Once they hold your message in their hearts, they can go back to their notes, your website, or your products for the mechanics.