The advice I wrote last year is good, but I thought of a new analogy: a PyCon presentation should be a trailer for your expertise. That is, imagine your expertise on your topic is like a full-length Hollywood movie. Then your PyCon talk should be the trailer for that expertise.
A trailer is by nature short, so is your talk. Not as short as a trailer, but shorter than you want. You have to think hard about what to take out and what to leave in. Like a trailer, your talk needs to tell a compressed story, it should have some relatable emotion in it, and ideally it will have some action (demos).
The point of a trailer is to convince people to watch the movie. The point of a PyCon talk is not to make people experts, but to convince them to learn more about your topic, which they can do afterward. You don't have to cram all the information into them, just as the trailer doesn't have to tell the entire story of the movie. If they leave thinking, "I'd like to know more about that," you've done your job.
Writing 25-minute technical presentations is hard, and this trailer analogy may not be perfect, but I think it's a good mindset to get into for crafting a good PyCon talk.