(1) Begin with knowing (significantly) what you are talking about.
(2) Be confident that you have something worthwhile to share/transfer.
(3) If indeed it is worthwhile to share and will help others; once you have convinced yourself of this; I believe your speech will flow most eloquently.
(4) Make it interactive; be not afraid to get your crowd interacting with your presentation as it is being presented.
(5) Smile, use different decibel levels and speak slower that you normally speak; this is important. If you doubt this watch MLK Jr. or John F. Kennedy's important speeches...
(6) Speaking slower or faster and quieter or louder and being more cheerful or more serious all adds dramatic effect and keeps the attention of your audience.
(7) Be not afriad of some repetitiveness. Repetition is necessary for information transfer... Martin Luther King was the absolute master of judicious repetition. For example: in his Washington speech of 28 August 1963, he used the phrases "I have a dream .." and "Let freedom ring ..." again and again (seven times and eight times respectively).
(8) A little humor in the opening sentences of a speech relaxes the audience and positions them onside with the speaker. Humor in the last sentence or two of a speech leaves the audience with a warm feeling towards the speaker.
(9) Make clever use of the pause. If you expect laughter or applause or you would like to create a sense of drama, pause for a couple of seconds, before continuing your speech.
(10) Whisper to emphasize significant points followed by repetition a "wee-bit" louder. This technique has been used to emphasize points in some of the major speeches of the 20th century...