Would you listen to a man whose speech you do not understand? It is unlikely, therefore, take care of their own diction. Only one loud voice enough to listen to you. And if you say, clearly, clearly, the audience of listeners is provided to you.
It is also important, as you say - we are competent, well-formed sentences. Learn the correct accents in words, read more, learn new terms. With an intelligent man is always nice to talk to.
Always be calm, likable. Nervous, screaming man is unlikely someone will hear. Even in the midst of an argument much more attention will be paid to him, said in a calm, quiet voice. So do not lose your temper and always remember what you are striving for in the long run.
Know what you're saying. We should not only deal with confidence in the subject, but also to understand what goals you are pursuing. Remember that sometimes change can not be someone else's opinion.
Be able to draw the attention of the listeners. Change your posture - if you're talking about standing up, it's a bit like when sitting - lean slightly to the audience. Do not be afraid to gesticulate. Use facial expressions.
If you're talking about fairly boring things, do not forget to be distracted. Then the public's attention will be totally focused on you. Tell the case of life or anecdote to this topic, please refer to the question to someone in the audience - such a lively conversation format will interest everyone, and your speech will not be ignored.