One of the biggest things that I notice right off the bat once a speaker starts is the speed at which they are going to talk. More often then not, folks speak why too fast. Slow down. If you feel like you are speaking too slowly it's probably the right pace. Breathe, it's ok to have a few seconds of silence. Repeat a sentence a few times. When doing a dry run, as a friend to listen to you and give you honest feedback on how fast you are speaking. Try to keep that even slow pace throughout the talk. The audience will thank you!
Less info on slides
This always seems to be an issue whether it's in person or virtual but virtually you have a whole other slew of issues to face when it comes to keeping people's attention. If you have too much information on your slide the attendee isn't sure if they should be reading what you wrote or if they should be listening to what you are saying. It's very difficult to do both and you can overwhelm people this way. Keep it simple. Simple images, less words.
Chapter vs. Whole Book
What's the big idea that you want to get across to the people in the "virtual room"? Let's note overwhelm them with every single thing that you have learned in your career ever. Think about speaking about a concept from a chapter of a book vs a whole book. A sprinkling of a few ideas from a couple chapters would be ok too but not every single idea and all the details that go into it. Don't try to jam pack your presentation with too much information or you'll lose them before you even get started.
know your audience
Not sure who's attending the event or virtual conference/summit? Ask the organizers! See if they can give you any demographics on who's going to be there. Re-read your abstract that you submitted when you applied to speak, what's the message that you are going to speak to that will land well with that particular audience. Can you make sure you aren't making too many assumptions on the their experience level? If you are speaking to mainly executives you would have a different message and takeaway with them then you would if you were speaking to junior developers.
demo? or not to demo?
To demo or not to demo, that is the question. I find demos difficult to graphic record, though I do it all the time, they can be challenging to follow and comprehend. I always wonder how much value that demo is bringing to the talk. I'm not saying don't do them, I just think there's a bit of thought should go into them before you go ahead with them. If people are going to have a hard time see all the small words and buttons on your screen you might lose them. If you don't have time and are rushing then you'll definitely lose them. Just think about it.