Research your topic. Take as much time as you can to be an expert in the subject area of your topic. This holds whether the speech is for a wedding, a corporate merger, an academic presentation or a political stump speech. It is important to know all the angles of the subject and to have facts straight. The fastest way to lose the confidence of your audience is to misspeak or appear confused.
Know your audience. Part of writing and delivering an effective speech is knowing the intended audience. The information you present -- including things like references, stories and jokes -- must be appropriate to the audience. Chances are you don't want to offend anyone, and you definitely don't want your references or subject matter flying over your audience's head.
Write several drafts and practice them. Write the speech as many times as it takes until it is something you are comfortable with. Have a friend or colleague edit it. Then, when you think it is perfect, read it aloud several times. This will help you become familiar with it and will reveal any awkward or misplaced passages. Edit it once more. Then read it aloud again, several times if necessary, until you are comfortable with it. Practice to make sure that it isn't too long or too short.
Arrive early. On the day of your speech, arrive early and know the room. Take a look at the placement of tables and chairs, at the lectern or podium, and at the audio equipment. The last thing you want is to get up to the lectern and find that it's up to your nose, or that the microphone doesn't work, or that you are obscured from the audience. Knowing the room will help make you more comfortable. If possible, try to practice the speech before the audience arrives.
Take a deep breath; remember your pace. Before delivering the speech take a deep breath and smile to yourself -- you know your material, you know the audience, you know the room. When delivering the speech try to pay attention to your pace. When nervous, people tend to speak faster than usual; this can make the delivery awkward and lead to a premature finish.