Silence is, in fact, useful when asking a question. Answer Gives audience time to think of an answer themselves. Vocal delivery also affects attentiveness. Speak normally, then at crucial point lower voice or speak slower. Introductions and Conclusions are the most important.
Research shows audiences listen more at the beginning and end of a presentation.
Above all, try to appear relaxed. You should, however, speak in full sentences. Make your transparencies interesting and easy to read. Use boldface, italics, etc. for emphasis. Organize your material carefully.