1. Do not overfill your speech with information. Remember that LESS IS MORE: the less information you convey, the more chances you will have to be able to convey them effectively.
2. The time allotted to your speech will be anyway too short to achieve more than one purpose. Thus, focus on what is really important.
3. Don't worry: Everyone knows you know a lot about your subject. In fact, everyone knows a lot about at least one subject. Thus, don't striggle to convey the impression that you could say much more than what you are actually saying. Focus on communicating instead.
4. Speeches are different than articles. Do not convey informations such as page numbers, editions, number of the sūtra, etc. No one will be able to take a note and if someone is interested, she will ask you at the end.
5. Don't read. It really makes a difference. It is hard t be boring and to indulge in the above mentioned mistakes once you are not reading.
6. Last, you might discover that questions and discussion are more fun than you might have thought. Be sure that you leave some space for that. It is often the more lively part of a speech and thus the one one remembers better.
I am surely forgetting something important (i.e.: I might not notice some of my most typical mistakes). Which habits of speakers do you dislike in particular?