Smile and be enthusiastic in tone, gesture and choice of words. Know enough about the subject to sound knowledgeable. Do not turn to the speaker and ask if the topic is epidemiology, epistemology or episiotomy. Announce the speech title as given to you by the speaker. If you have any questions about it, ask the speaker before the introduction.
Many speakers select specific titles for a reason or for a pun.
If the speaker is not using a title, make sure that your description matches the speakers. Introductions are no place to use slides, overheads or presentation software. Anecdotes are good but should pertain to the subject and be in harmony with the mood of the presentation. Avoid using canned jokes. If the credentials of the speaker are so outstanding that they must be shared with the audience or if there are publications the audience will want to know about, insert them in the program or prepare a separate commemorative handout.