Very specific things are required of a good speech. First, a good speech must contain correct information on the subject the speech revolves around. A speaker must do his or her research and know the topic well. A speaker must also be sure not to include too much logos (logic) or pathos (emotion). A speech which contains too much logos may bore the listener. On the other hand, a speech which contains too much pathos may cause the listener to feel as if the speaker only depends upon emotional appeal and no logic. A speech should contain a healthy balance of logos, pathos, and ethos (credibility). The inclusion of ethos insures that the speaker is trustworthy and possesses creditability.
A good speech contains no vocal/verbal pauses (um, ah, uh, you know, repetitive ands). Vocal/verbal pauses show that the speaker has forgotten what comes next in the speech (illustrating that the speaker is not completely prepared).
A good speech does not lead listeners astray, circle around truths/falsehoods, or intentionally provide incorrect information. A good speaker looks his or her audience in the eye.
Essentially, a good speech will be one that is will thought out and researched, practiced, contains the right balance of ethos, logos, and pathos, and leaves a call for action for a listener (if necessary).