Offer any major alternative explanations for your data, and offer counterpoint arguments. Remember that a significant portion of your audience may be thinking along similar, alternative routes. Make your figures large enough to be read at the back of the room. Point to the screen not to the overhead projector. Speak to the audience, not to the screen or to the projector.
Eye contact is important in keeping an audience engaged.
Show enough data to demonstrate the point, but we don't need to see every blot you've ever done. At the end of the talk, summarize your results and draw conclusions. Project future experimental questions raised by your research. A credit slide is fine, but don't spend inordinate amounts of time thanking people at the end. Your audience comprises busy people.