Build the presentation "up," but start by building the narrative "down"
I argue in all my lectures and classes that a slide presentation needs to be built "up" from a core narrative. That is, define a simple narrative and add slides consistent with the time you have and the ability of the audience to understand complexity. Try developing a 3 minute presentation, a 5 minute presentation, etc. In other words think about what you can add, not what you can cut.
But the process of defining that core narrative works the other way. The first attempt at a narrative is likely to contain a lot of jargon and complexity. Try it out on a close colleague (person at the next lab bench) and he/she will tell you parts that they don't understand. Then try it out on a colleague with a little less specific knowledge (person in the next lab) of your research. Keep moving "down" the ladder of expertise until you can explain the narrative to what I call the least knowledgeable target listener. Not everyone, but the least knowledgeable person you hope to engage.
This two way flow is illustrated on the following slide. Narrative development is in blue, slide development in orange.