That said, I'm not really a "keynote" speaker. I've been doing it for most of my adult life, in front of small and large (but never huge) crowds.
I've definitely had some bombs, but most folks seem to think I do an adequate job (the fact I'm not a rubber chicken speaker means that it isn't much more than "adequate." I'm fine with that).
Most times, I wing it, but when I'm giving an important talk, like a tech class, or topic discussion, I practice. The tip someone gave about recording themselves is good. It's also how I know how long it will take. I'll often use a prompter app, while practicing, but don't use it, while giving the talk.
I've found a bit of humor (especially self-deprecating humor) can "humanize" things, but it should be short vignettes, and know your audience. If I don't really know who will be out there, I generally don't use humor. Most times, I know my audience quite well, and humor is appreciated.
I have found that speaking in the vernacular is generally appreciated by folks. There are definitely some folks that don't like making difficult stuff easy to understand, but I'm just an ol' high school dropout with a G. E. D., so I don't really pull off the "talk purdy" kind of thing, so good.
I've found that Keynote/PowerPoint shows can be useful, but I seldom use "wall o' text" slides. I use a lot of images and animations, and pack my notes (not the slides) with what I'm saying. I will usually insert
-- CLICK --
I'll put details and technology rabbitholes into the supergraphics.
People have widely varying views about what a “conference” is, or should be:
It's very nice to have a few people come up after a talk with "I saw what you did there...". It's a great way to connect with people who are on your wavelength.
One or two well-placed jokes can be great if they’re a very minor part of the presentation.
When someone has their slides stacked with memes or spends large amounts of time on vacuous entertainment content, it always feels disappointing.
There was a period of time where our biggest local JavaScript conference felt like one big entertainment competition. Presenters were singing songs, playing guitar, showing several minutes of clips from TV shows, and telling jokes more than they were presenting anything useful. The conference was a hit for young people and juniors, but it became known as a big waste of time for everyone else.