Decide the one thing they must leave with

Before anything else, write one sentence: if they forget everything else, what must they still know or do? Almost every bad presentation is one where the speaker had four things to say and gave equal weight to all of them, so the audience left remembering none of them.

That sentence then governs everything after it. Anything not building toward it comes out, however interesting it is and however long it took to prepare. Cutting good material that does not serve the one thing is most of the skill.