A presentation is a prepared talk given by a speaker to one or more listeners. To be effective, the speaker's message must pass to the listeners — it must be heard and correctly understood. In general, two-way communication is more effective than one-way communication; so, encourage the audience to participate — by asking questions or making comments. In any case, remember that the talk is given for their benefits — not for the speaker's.

effective organisation of information
effective delivery of information
effective use of language
never forgetting your audience
allowing participation through questions or comments

Transparency of structure (have a clear beginning, middle and end)
Organisation of content (clearly identify the main points and supporting points)
Level of information (start in the audience's area of interest)

Image (decide whether to appear formal or informal, relaxed or high-powered?)
Audience features (know their interests?)
Nonlinguistic techniques (use suitable body language and eye contact)
Linguistic techniques (pay attention to voice audibility and clarity, variation in pace and pitch, pauses, questions and humour)
Technical support (use of visual aids, e.g. slides, flip chart, transparencies and PPTs)

Vocabulary (choose the right word for spoken rather than written language)
Grammar (assemble the sentences in correct language forms)
Pronunciation (stress words correctly)
Fluency (variation in sentence structure and length)
Speed (link your ideas, and don't talk too quickly)

A brief introduction is always given at the very beginning of the presentation. It should include at least four pieces of information:

What you're going to talk about;
How long you'll take;
What your main parts or sections will be;
Whether you'd welcome questions during your talk, or only at the end.

This could take as little as 45 seconds, but it will give you time to establish contact with the audience. Don't only try to impress them by your organisation and obvious preparation. Go out of your way to make some comments on the present situation (e.g. excellent lunch, weather — anything which shows awareness of the world outside your subject). Beware of jokes, and make as much eye contact as possible. If necessary, give a few facts about yourself and the purpose or background of your talk.