First time preacher. Verily, verily!
Well, you should remember that preaching, first of all, is an extended testimony with the intention to teach, rebuke, exhort, or all of the above. As such, it is as much a personal revelation to the speaker, as it is a revelation to the listeners. About teaching in general however, read the book of Titus 2. Paul teaches his young protege on how to teach.
In everything set them an example by doing what is good. In your teaching show integrity, seriousness and soundness of speech that cannot be condemned, so that those who oppose you may be ashamed because they have nothing bad to say about us... These, then, are the things you should teach. Encourage and rebuke with all authority. Do not let anyone despise you. (Titus 2:7-8, 15)
Fire and Passion is optional, it depends on the type of person you are. I know good pastors who speak slow and deliberate, while some speak in monotonous drawls, while some speak in fiery arguments. Yet they remain good not because of such, but because of what they speak. And what they speak is undoubtably God's Word.
Practical advice though, in public speaking:
1. Choose a subject you are passionate about. Think about it. Deliberate. The more passionate you are, the more you can address it with fire.
2. Prepare. Write it out, put it in a tablet, a piece of paper, in bullet form, and perhaps also put it in a powerpoint presentation. The small delays in changing frames and reading what you wrote in the screen gives you precious seconds to catch your thoughts.
3. Speak slowly and clearly. Precious seconds. Also, this is what Paul says about speaking Soundly, and Serious. There are some pastors that use jokes, but those are just used as punctuations in the speech. It is in the serious moments that God's spirit can convict a sinner to repent.
4. Prepare a few stories that would best portray your subject. Make sure it is relate-able. Some can be funny, some serious. That said, don't joke if you don't have the talent for it. Or else: awkward silence.
5. Address the audience directly. If you know someone in the audience, speak as if you were speaking to them. This allows contact. Choose three, one in your left, one in the center, one in your right.
6. Have authority, as Paul says. Now, don't misunderstand this authority. Don't use the pulpit to boss around, but speak as if you know what you are talking about. Don't give them doubt that you are anything but authentic.
7. Empathize. Remember that you must balance encouragement and rebuke. I know some pastors that like rebuking too much, even when it's the time to encourage a discouraged Christian. Suffice it to say that their preaching would have an ill effect because of that lack of empathy.
8. Pray. Yeah. Very important this one.