The Power of Three
The effectiveness of the "Power of Three" is well-known among speechwriters. There are some psychological reasons why humans like the number three, but it's not important that you know why, it's just important that you use it to your advantage.
(But don't shoehorn this into situations where it isn't appropriate. If you've got four reasons for doing something, don't shorten the list to three just because it's a more powerful number. And if you overdo the power of three so that it becomes noticeable to your audience, then it's not a help, it's a distraction. So use the power of three only when it makes your speech better.)
The power of three can also be used to humorous effect. When you list two items, followed by a third that is NOT what the audience anticipates, it's unexpected and can be quite funny. An example would be "the three greatest works of American fiction are The Catcher in the Rye, Adventures of Huckleberry Finn, and a politician's campaign promises!" Or the observation "There are three kinds of people: those who make things happen, those who watch things happen, and those who wonder what happened." Or Benjamin Disraeli's "There are three kinds of lies: lies, damned lies... and statistics."
Again, don't overuse this technique. Using it once every minute or two ― whether for emphasis, dramatic effect, or humor ― is probably sufficient. But carefully and appropriately used, there are few speaking techniques that are more effective than the Power of Three.