Peter Mead suggests some hints and reminders.  I summarise them here:-

1. Preach one big idea.

2. Structure your thoughts.  Let there be clear, simple, logical progression of ideas.  If you know where you are going, it is more likely your listeners will travel with you.

3. Get rid of unnecessary content.  Every message needs some time in the cutting room.  Remove anything – however interesting or useful – that is superfluous to your goal of communicating your main idea effectively and clearly.  Clarity comes from expulsion of unnecessary content. Every message needs some time in the cutting room.

4. Choose words that communicate.  Your goal is not to impress, but to instruct.

5. Repeat important words (and, I would add, use well-selected synonyms in order to drive home your ideas.

6. Restate important sentences.  Give people another chance to grasp key sentences.  Add interest and impact by varying the wording.

7. Manage your transitions.  It has been said that we tend to lose people in the turns, so drive carefully.  Make transitions clear and obvious, pause, re-engage, and then move on.

8. Use variety in delivery.  Vary the pace and the pitch at which you speak.  Practice adding emphasis by vocal means.

9. Use physical movement effectively.  Monotonous or bizarre gestures distract, but appropriate movement can clarify the message.

10. Effectively engage the listener.  Energy and enthusiasm help here.  Look up, and check that your listeners are engaged with you as you speak.