Hi Abtari,
Speeches can be "good" for a number of reasons; they can be humorous, emotional or simply straightforward. The most important thing you must remember though, is that in making a speech, you're trying to draw the attention of your audience, continually. You have to adopt a register that suits your audience. Eg, if I was making a speech as a Nobel Laureate speaking about my work, my language would be very technical and be supported by jargon. Contrastedly, if I was making a speech to a group of (junior) high school students, my language would be more colloquial, and I'd include more humour or dramatic elements that my audience can relate to.
It's also wise to adopt a personal approach eg:
Luther King : I had a dream...
Antony: Friends, Romans, Countrymen
Atwood: my daughter...
In order to sustain your register, you should employ language techniques such as rhetoric (eg questions with an "obvious" answer), exlamation, emotive tones and imagery (eg the vision of Luther King)
This when combined with a solid structure, as Jhakka already explained, should be all you need.