Choose a theme. You must know who your audience are and think of ONE thought you want to leave your audience so that they will have a greater tendency to remember it.
Utilize theme reinforcers or points to support the central idea(theme) they are trying to get across.
Wrap it all together. You can arrange it first in outline form. Numbering your points could also help the audience remember where you are. Always return to theme and leave everyone with an impact in the climax of the speech.
Quotes, resources and an unconventional idea can be incorporated to speeches to gain the attention of your audience.