Visualize your presentation as a starfish. Your central message is the middle and your main points radiate our from there. If you get off track, just return back to the center.
Sarah Gershman points out that a speak needs a central message. She writes that:
Next time you prepare your content and each and every time you practice your speech, first review the central message of your presentation. You should be able to state this in no more than one sentence.
If you can create one sentence that sums up your core message it will be much easier for your audience to remember.
I like the starfish as a symbol for a speech. There is a central part, your core message, and the arms represent a handful of points you want to make.
Credit: Photo Starfish on the Beach.