* Always give an overview - a complete, but low-resolution version of the whole picture. Identify key parts of the picture by name and use those same names when you get into more detail
* Number and name things. If there are 3 points, tell people there are 3 points. Then cover them...1, 2, 3. Don't get into sub-points like 2.1, 2.2 so that people lose track of the fact that there are 3 points.
* There's an old mantra that goes "Say what you're going to say; say it; then say that you have said it". That's 100% the way to go imo. Tell people "I'm going to give you a quick overview of the 3 main points first; then I'll go into detail on each of those 3 points. That'll take longer. Then I'll recap in case anything is still unclear, then we'll have Q & A".
* When you transition from one thing to another, refer back to the outline you established so that people know where they are on the map, i.e. "So much for point #2. Now, point #3...". Or "So that's the 500-foot view. Now I"ll go through each of these points in more detail...".
* Don't try to anticipate the questions too much. You'll be wrong about what what's going to give people difficulty no matter what, so listen to how people react and adjust accordingly!