As a public speaker, it's important to follow some basic rules as you approach the crafting and delivery of your speech. These rules include ethical goals, full preparation, honesty, and non-abusive language.
Consider why you're speaking. Are you trying to persuade your audience to adopt a certain viewpoint or consider a new idea? If so, you'll want to make sure that you lead your audience to that belief point in an ethical manner. You don't want to use tactics like intimidation. Additionally, have the responsibility and professionalism to know whether or not you have a conflict of interest on a given topic or with a certain audience or venue. Recuse yourself--provide your audience with a full disclosure of said conflict of interest, and adjust your speech accordingly.
Effective speakers are those who take the time to fully prepare their speeches, from the speech writing process to the delivery of the speech to the very clothes they wear for the speech. If you don't prepare, it will show and ultimately affect your credibility as a speaker to your audience and colleagues. Respect your audience by taking thorough time to write, edit, review and rehearse your speech before presenting.
Honesty is an extension of the ethical goals of your speech. Don't resort to falsehoods or opinions presented as facts to make your case. Come from a place of authenticity instead of deception. Your credibility can become damaged when it is revealed you have either lied or even just slightly bent the truth in your speeches.
Just as one shouldn't intimidate his or her audience, one should refrain from abusive language when speaking in public. This means attacking your audience verbally, or, in a debate-style setting, even verbally attacking your opponent. Don't resort to name-calling or bullying; rather, make your case through the use of compelling facts and anecdotes that can be substantiated.