Theme: Determine what point you want to drive home—this is your theme. Write it down--it will be like a beacon on a lighthouse guiding you through your speech development.
Main Stepping Stones: Determine what facts or viewpoints support the theme. Try to write down at least 3 facts/viewpoints. Leave space between each fact/viewpoint. (Most impromptu speeches are typically 2 to 5 minutes. If the one you are called upon to deliver is longer, you may need more facts.)
Supporting Material: Under each fact/viewpoint, use at least two or more of the following:
- Supporting argument
- Authoritative quote(s)
- Reasoning points
- Humorous aside
Order & Transition: After you have all that in front of you, order your points by relevance and impact by putting large numbers alongside the main points. This will be your ad-hoc outline & speech order. Quickly think of how you can transition from one fact to the next.
Do not expect to have a word-for-word memorized speech when you get up to speak. Instead, envision a garden path with each main fact being a section of that garden and the supporting points being the various flowers in each section. The exercise of impromptu speaking is designed to teach you to think on your feet. Use your quick outline to keep you on your path.
Especially in regards impromptu speaking, one thing instructors in speech classes are looking for, although they won't tell you so, is your ability to ad-lib fluently. Being able to throw in humor that helps drive home a point is actually the mark of an accomplished speaker. For example: "Some people say that animals go to heaven too. Well, my dog went to heaven but couldn't find a tree to mark. It was hell for him."
Another approach helps add time and coherency to your speech: First tell them what you are going to talk about (introduction), then tell them what you have to say (body), then tell them what you told them (review and conclusion). This helps a speaker reuse the same material but in a completely acceptable way.
If you are a student of the Bible (as I am) engaging in secular or academic speech (as I did in Toastmasters), there is nothing wrong with citing a scripture. Perhaps a proverb, principle, or Bible story with a lesson (parable) that relates to the subject. If you frame it in the context of yet another opinion, no one can fault you for using the Bible because it is just as valid a source as is any other authority. If you decide to incorporate a scripture, make sure to highlight it’s practical application and reasonable value.