It seems that certain rhetorical devices work much better than others to improve the sound quality of text/speech.
Here, I have listed some rhetorical devices commonly used by best/popular speakers in history and in present.
1. Repetition
Repeating part of sentences. For example, three sentences that each have same first part.
"You can hunt us. You can bombard us. You can even kill us. We will never capitulate."
Notice that in 3 sentences, the words "you can" is repeated 3 times.
The word "us" is also repeated 3 times.
So in those 3 sentences, first and last parts are same in all 3 sentences.
You can choose to have same first part in each sentence, same middle part or same ending part, or some combination of these.
Same first part is called anaphora.
Same last part is called epistrophe or epiphora.
Repetition of words or groups of words isnt the only way. There is also repetition of sounds and letters in sentences, same letters at start of words.
These are usually alliteration, assonance.
2. Parallel structure
Parallel structure has many forms, but it usually refers to two or more sentences having same structure of verbs, nouns, logical connectives...
It also includes equal distribution of words per point/paragraph. For example, if points are health and costs, both should get somewhat equal number of words, equal attention.
Usually, its best to keep paragraphs short because people dont like to listen too much about same point. Its better to have many points than spend whole time talking of just one.
3. Contrasting ideas
People like to hear opposite ideas being presented to them. For example, mentioning something good about opposing side and then turning it against them, using sarcasm and such.
Comparison is very useful in speeches.
4. Insults
As strange as it sounds, many popular speakers use insults or mocking to make a point, and this makes their speech more entertaining. Of course, you shouldnt use insults on Dart where its banned.
5. Probability argument
This is a very important part of debates, since even if some argument isnt proven fully, if it is probable, it becomes almost as just as good as proven.
6. Analogy
Analogy is very important because it makes the audience think there is contradiction in opposing side.
7. Deductive and inductive reasoning
Both are very important.
Its important to have general facts which create specific conclusion.
It is also important to have specific example which creates general conclusion.
Examples are very good way of making speech effective. Statistics are even better, since they are general.
8. Story
Story, personal story, any story really, adds emotions to speech so its not just dry facts. People are not attracted to dry facts alone, which is why top scientists rarely become presidents.
9. Humor
Your speech should be funny. Comedy is usually expressed in form of mocking some person or idea by exposing absurd things in it.
10. Playing on emotions
Playing on emotions such as fear, hope, pity, compassion, authority, loyalty, trustworth, character... are all ancient ways of making speeches that still prevail today.
11. Climax
This is very important in speeches. Basically, your speech should be created by order of importance. You talk about less important things at start, and then move to more important things, speech points sorted by order of importance.
If this rule is not followed, for example if someone talks about most important point at start, and then moves to less important things, his speech will be only interesting at start, but later it will become more boring since significance of points decreases.
12. Common ground and shared beliefs
You cannot win any audience if you try to just impose your views on them. Instead, you must use beliefs and values they have to support your arguments. For example, if audience is made out of vegans, you are not going to get anywhere by promoting meat, but promoting animal rights will hit the spot.
13. Focus on praise and blame
Basically, you are supposed to blame opposing side for bad things, or praise your side for good things, or both.
This is called epideictic speech.
14. Understatement and overstatement
Its very important to overstate all good things of your side and all bad things of your opponent's side, while understating all good things of your opponent's side and all bad things of your side.
15. Prove by negating opposite
Its crucial in speech to convince audience that your position is the only good option. This is done by negating opposite options.
16. Logical axioms, reason, facts, observable evidence, statistics, expert opinions, examples
The easy way to write speech is to gather all these to support your side.
Also, writing down general arguments which apply to most debates is very beneficial.
17. Stick to topic, no rambling
Your speech should be organized into separate points that all support topic.
18. Linked/chain events
This is very important part of speech. For example, saying that paying teachers more improves education. Improving education reduces crime. Reducing crime improves economy and reduces deficit.
Same can also be used to attack opponent's arguments.
For example, pointing out result of opponent's position, expressed by linked events.
19. Use pauses
Pauses are very important in speeches, not just to allow audience to clap, but to give them space to process spesch easier. Same works with text. Paragraphs should be spaced.
20. Rule of three
Rule of three is important in speeches. Saying 3 points to support one argument, or saying 3 things like "we need peace, freedom and happiness" usually adds sound quality to speech.
