Be sure that the font size is sufficiently large to be read by everyone in the room. An outline of the talk. A general location map, where applicable. Clear legends, scales and other items relevant to each diagram. The figures should not be cluttered, but should contain only that information which is necessary.
Mathematical formulas are few, clear and simple.
For each slide, it may be helpful to write down the main ideas on a separate sheet that is handy. The day of the talk Visit the room in advance and check the layout. Verify the use of projectors, microphones, pointers. Delivering the talk Rehearse in front of your colleagues, and consider their comments seriously because they will be trying to help you. Allow enough time for each slide to be deciphered and understood.