When mentoring new technical speakers, I like to cite what I call "the 10% rule".
Think about it like this: If you are presenting on a 100-level topics (for example, "Intro to Angular" or "Building Your First App with Elixir"), you can safely assume that your audience is one of three types people.
First, they are an absolute newbie who is there because they heard about this technology but have practically no experience with it.
Second, they have been to previous talks on the subject or have read a couple tutorials. They are not starting at "ground-zero", but they are darn close.
Third, they are seasoned or beyond 100-level, and they are looking to see if you offer new perspective.
The 10% rule applies to the first two groups. Your job as the presenter is to try to leave the audience with 10% of the knowledge you have on a subject.
Ten percent sound like a lot, right? Doesn't have to be. For most developers, this is seeing how pieces lay together or how do you do something from scratch.
Ten percent might simply be "what problem does the thing I'm showing you solve?"
My first set of presentations were around jQuery (2007 era). My intro talks discussed manipulating the DOM and listening for events. I'd discuss the "hard" way, but then showed how easy jQuery made it.
If you're adventuring into 200 or 300-level talks, the same 10% rule can apply. Imagine you want to do a talk on "new C# features". Your expectation is that the audience is familiar with C#. Your 10% is going to be a simple list of what is new, with basic explanations.
If the attendee goes home and runs into a scenario where a new feature would be useful, you have provided them with the foundation to research more.
The 10% rule is meant to build foundations for learning. Expose audiences to ideas and concepts, and guide them towards better self-learning.