When a person is about to deliver a speech there are a few things that should go through his mind, the basics of a good speech are not very complicated, the speaker has to show the audience that he is knowledgeable and proficient in the subject of the speech, and if the speaker can inspire the audience and make it respond to the things he is saying, it will be considered an overall good speech. There are those who are extremely talented in speech making and will not only awake the audience but strike a strong impression on it.
Most of the people are not very happy about making speeches or giving even simple presentations to a small group of other people, this can get even worst if the audience is made of people that the speaker does not know, and almost catastrophic when these are people who judge the speaker. This is no big surprise since we know that the stress related to performance and quality of presentation is huge, most people seem unable to unassociated themselves from the pressure of giving a good performance.
The most basic thing to work on before giving a speech is to relax and understand who are the people you are about to speak to, why they are there, what are their motives and areas of interest and what is it they are looking to get from the time they will spend listening to you. Once you manage to really comprehend these factors you will be on your way to giving a better speech.
When someone is required to give a presentation while at school the main idea is that the student will be presenting a case in front of other students and usually one teacher, the teacher will judge the students ability based on the performance given, this is a huge source of stress to begin with, but there are ways to diffuse this tension. A good speech does not necessarily mean that all the time of the speech has to be dedicated to the topic, if by going off the topic the speaker can manage to control the crowd better it is advisable that he attempts to do that, in many cases the control over the audience will score major points with teachers and students, and a key way to prepare for a speech that hold off topic points in to focus on 4 or 5 related, but not the same, topics.
If the presentation is done in the workplace than it should be relatively easier for the speaker to present a good speech if he can convert the speech into a business talk like situation, a good way of thinking about it is like you are sitting on a train heading to work and a nice interesting person is sitting besides you, you engage in a talk and the other person asks you different questions about your work, once the conversation is going the questions start to focus deeper and deeper into your specialized fields, this is a way to approach a presentation to other business colleagues, it is simply a talk in which you explain some key basic points about your work.