There are good ways and bad ways to make a lecture with presentation equipment. Here's the way to flop (you didn't expect that, did you?):

Arrive late

That would certainly be foolish.

You should come on time, to make sure that everything is connected and working properly, to get used to the hall, and to practice on the same stage as you'll be lecturing later on.

Even if you are just giving a small lecture in a classroom, you don't want to flop. Get there early enough to get used to the place, and to be comfortable.

Don't practice

Some people are under the illusion that the presentation software will do their work for them, so they don't have to rehearse in advance.

Others don't do the necessary research about their audience, and the proclivities, knowledge, expereince, preferences, and background of that audience.

Every speech should be tailored to the specific audience. If you just get up and give a canned talk, you'll be canned.

Ignore the audience as they arrive

Well, this is related to the item about getting there early.

You should stand in the way of your audience as they arrive, so that they have to shake your hand. Make sure that there is only one entrance door - and if fire regulations don't permit it, then place people to block the other entrances during the initial phase.

Try to impress them with your big words

They won't be impressed. They won't even pay attention. They aren't going to struggle to understand your words. They will just ignore them.

Well, maybe they will be impressed by your intelligence, but they won't come away with the message you are trying to present.

But aren't you there in order to share your message?

Run away

If you show that you are too busy to talk to them afterwards, you'll miss a great deal of their imprtant feedback.

Don't put on airs when you remain. Be a part of the audience - relaxed, friendly, and pleasant.