Here is what I do to become a good speaker which may help you too.
1) Watch this Bill Clinton video from start to finish and make notes on what he does well in connecting with people. I think this is one of the best persuasive speech ever give in a high-stakes situation.
2) Watch our speech analysis of Bill Clinton's speech. To become good you have to analyze a speech like the way do here.
3) Read the blog that I wrote on why I think this is a great persuasive speech. You have to be able to teach others. Note, to become a good speaker, you have to be both a student and a teacher.
4) Watch the speech again
5) Now go record your speech and keep practicing.
If I come across anymore I will add it here, but that is all I have right now and there is a lot here. It is not that complicated. Learn from the masters of public speaking and study them and try to emulate them till you develop your unique style. That is how everyone who has ever become great has done it.